This Study Guide ties together number theory, revolutionary France, American songbook standards, 1980s film comedy, Horn of Africa geopolitics, climate PR, and fast-food empires. The Year I puzzle hinges on the French Republican calendar (1792–93) and the fact that primes greater than 5 must end in 1, 3, 7, or 9, giving 1793 as the year when Year I ended.(en.wikipedia.org)

From Irving Berlin’s 1926 song “Blue Skies” (later covered by Ella Fitzgerald and Willie Nelson) and adopted as a skydivers’ good‑weather greeting, to Chevy Chase’s alias-spinning reporter in Fletch (1985), today’s questions show how trivia often lives at the intersection of pop culture and subculture.(en.wikipedia.org)

We also visit Djibouti, the city-country port lifeline for landlocked Ethiopia since an 1897 Franco‑Ethiopian accord, trace how BP and Ogilvy popularized the term “carbon footprint” in the 2000s, and watch Raising Cane’s grow from a single LSU‑adjacent chicken shop (1996) to a 900+ location, $5+ billion chain.(fr.wikipedia.org)

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Study Notes

Question 1: French Republican Calendar & Prime Digits

Every prime number greater than 5, when written in base 10, must end in one of four digits. A four-digit number using each of these digits exactly once gives the year that marked the end of Year I (1) in the French Revolutionary Calendar. What is that year/four-digit number?

Year I of the French Republican (Revolutionary) calendar ran from 22 September 1792 to 21 September 1793, so it ended in the Gregorian year 1793; those four digits are exactly the possible last digits of any prime greater than 5 (1, 3, 7, 9).(en.wikipedia.org)

Connections

  • Why primes must end in 1, 3, 7, or 9: Any integer ending in 0, 2, 4, 6, or 8 is divisible by 2, and one ending in 5 is divisible by 5, so primes greater than 5 can only end in 1, 3, 7, or 9 in base 10.(en.wikipedia.org)
  • Year I as a political reset button: After the monarchy was abolished on 21 September 1792, revolutionaries declared the next day (22 September 1792) to be 1 Vendémiaire, Year I, symbolically restarting history at “Year One” of the French Republic—a metaphor later reused for other revolutions.(en.wikipedia.org)
  • The calendar’s cultural afterlife: Month names like Thermidor and Brumaire now double as historical shorthand: historians talk about the “Thermidorian Reaction” (the conservative swing after Robespierre’s fall on 9 Thermidor Year II), and Lobster Thermidor and Neil Gaiman’s Sandman story “Thermidor” both riff on the period’s imagery.(en.wikipedia.org)
  • Napoleon and Republican dates: Key early moments in Napoleon’s rise—such as his suppression of a royalist uprising on 13 Vendémiaire Year IV (5 October 1795)—are often dated in the Republican calendar in scholarly works and captions to revolutionary-era art.(en.wikipedia.org)
  • Last digits and deeper number theory: Modern research on prime distributions shows that, asymptotically, primes ending in 1, 3, 7, and 9 are equally common; subtle biases in how these digits follow one another are an active research topic.(en.wikipedia.org)

Sources

Question 2: “Blue Skies” and Skydiver Slang

What two-word phrase, used by skydivers as a greeting wishing good weather for safe jumps, is also the title of a cheerful 1926 Irving Berlin song, later popularized by Bing Crosby and Danny Kaye (1954), Ella Fitzgerald (1958), and Willie Nelson (1978)?

“Blue Skies” is a 1926 popular song by Irving Berlin, written for the musical Betsy and since then recorded by many artists; the phrase “Blue skies” is also a standard skydivers’ greeting meaning good weather and safe, enjoyable jumps.(en.wikipedia.org)

Connections

  • From Broadway to jazz standard: Berlin composed “Blue Skies” as a last‑minute addition to the 1926 musical Betsy; audiences demanded some two dozen encores on opening night, and the song quickly became a hit and part of the 1920s jazz standard repertoire.(en.wikipedia.org)
  • Early film history: Al Jolson sings “Blue Skies” in The Jazz Singer (1927), one of the first feature‑length “talkies,” helping cement the song’s place in film history.(en.wikipedia.org)
  • Star-studded covers: A 1946 film musical titled Blue Skies starred Bing Crosby and Fred Astaire; Ella Fitzgerald’s 1958 version on Ella Fitzgerald Sings the Irving Berlin Song Book brought virtuosic scat improvisation, and Willie Nelson’s 1978 country cover hit No. 1 on Billboard’s Hot Country Songs chart.(en.wikipedia.org)
  • Skydiver greeting: At dropzones, “Blue skies” works like “aloha” or “hang loose”—a hello, goodbye, and wish for clear weather all at once; skydiving schools explicitly teach the phrase as core lingo.(skydivecarolina.com)
  • “Blue Skies, Black Death”: Skydivers use the motto “Blue Skies, Black Death” (often shortened BSBD) both as a memorial toast when a jumper dies and as a reminder of the sport’s risks; the phrase titles lectures, songs, and true‑crime stories about skydiving fatalities.(scholarworks.bgsu.edu)

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Question 3: Chevy Chase’s Alias-Happy Reporter in Fletch

Don Corleone, G. Gordon Liddy, Dr. Rosenrosen, Arnold Babar, and John Cocktoastin are among the aliases used by the titular investigative reporter in what 1985 comedy?

These are joke aliases used by Irwin M. “Fletch” Fletcher, the undercover Los Angeles reporter played by Chevy Chase in the 1985 comedy-thriller Fletch, adapted from Gregory Mcdonald’s 1974 mystery novel.(en.wikipedia.org)

Connections

  • Source material and awards: Mcdonald’s novel Fletch introduced the wisecracking investigative reporter and won the 1975 Edgar Award for Best First Novel; its sequel Confess, Fletch also won an Edgar, the only time a novel and its sequel have won back‑to‑back.(en.wikipedia.org)
  • Alias wordplay: Fan-compiled lists document Fletch’s rapid‑fire pseudonyms, including Don Corleone (a nod to The Godfather), G. Gordon Liddy (the Watergate conspirator), Dr. Rosenrosen / Rosenpenis, Arnold Babar, and variations on “John Cocktoastin”—all underscoring how the movie leans on pop‑culture and political in‑jokes.(geocities.ws)
  • Cult status and influence: The film blends noir plotting with deadpan comedy and has built a cult following; later works parody its undercover‑reporter shtick, such as the wolf reporter in the animated film Hoodwinked! who explicitly echoes Fletch’s disguises and even uses a similar musical theme.(en.wikipedia.org)
  • Continuing the franchise: The original film spawned Fletch Lives (1989) and, decades later, a rebooted adaptation of Confess, Fletch (2022) starring Jon Hamm, showing the durability of Mcdonald’s character.(en.wikipedia.org)

Sources

Question 4: Djibouti – Ethiopia’s Maritime Lifeline

Among the world’s cities that currently share their name with the country in which they are located (such as the city of Luxembourg), which one served as the official port of Ethiopia beginning in 1897?

Djibouti (Djibouti City), capital of the Republic of Djibouti, became Ethiopia’s principal maritime outlet after an 1897 Franco‑Ethiopian agreement granting Ethiopia free movement of goods through the port, and it remains the main seaport for Ethiopia’s foreign trade today.(fr.wikipedia.org)

Connections

  • Same-name capitals: Djibouti City is one of a small group of capitals that share their names with their countries—others include Luxembourg, Monaco, Kuwait City, Panama City, San Marino, Singapore, and Vatican City.(lesleyslists.com)
  • Railway and empire: Work on the Franco‑Ethiopian railway from Addis Ababa to Djibouti began in 1897 and was completed in 1917, tightening Ethiopia’s economic dependence on Djibouti’s port and cementing the city’s role in regional trade.(en.wikipedia.org)
  • Modern geopolitics: Today Djibouti hosts several foreign military bases and handles the vast majority of landlocked Ethiopia’s imports and exports—over 90–95% by many estimates—making the city a crucial node in Red Sea and Indian Ocean shipping.(en.wikipedia.org)
  • Djibouti in fiction and film: The port and surrounding deserts feature in Elmore Leonard’s novel Djibouti, about documentary filmmakers covering Somali piracy, and in acclaimed films like Claire Denis’s Beau Travail, which follows French Foreign Legion soldiers training in Djibouti.(en.wikipedia.org)

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Question 5: BP, Ogilvy & the “Carbon Footprint”

In 2004, BP hired advertising agency Ogilvy & Mather to popularize what two-word term for the measure of an individual’s personal contribution to climate change? Coined in 1999 but relatively obscure until this campaign, the phrase is now common—though critics argue BP’s intent was to shift public focus away from fossil fuel companies and onto consumers.

“Carbon footprint” is a measure of greenhouse-gas emissions associated with an activity, product, or person; the phrase was coined in 1999 but became widely known after BP and its agency Ogilvy used major campaigns and online calculators in the mid‑2000s to promote personal “carbon footprints,” a move many scholars interpret as shifting responsibility from fossil‑fuel producers to individuals.(en.wikipedia.org)

Connections

  • From “ecological footprint” to “carbon footprint”: The broader concept of an ecological footprint was developed by William Rees and Mathis Wackernagel in the early 1990s as a way to quantify human demand on ecosystems; journalists trace “carbon footprint” as a derivative term first appearing around 1999 in British media.(en.wikipedia.org)
  • BP’s Beyond Petroleum campaign: BP’s early‑2000s “Beyond Petroleum” rebrand included ads and web tools inviting people to calculate and shrink their personal carbon footprints, with Ogilvy credited for developing the carbon‑footprint framing and a 2005 TV ad series explicitly titled “Carbon Footprint.”(en.wikipedia.org)
  • Critiques of responsibility-shifting: Climate communicators and historians like James Morton Turner, Geoffrey Supran, and Naomi Oreskes argue that carbon-footprint messaging emphasized “routine human activities” over corporate decisions, paralleling tobacco-industry strategies that individualize blame.(en.wikipedia.org)
  • Everyday life and labels: Today, carbon-footprint calculations appear on everything from airline offset tools to food labels, and organizations like the Carbon Trust certify product and company footprints, showing how a once-obscure phrase has become embedded in consumer culture.(en.wikipedia.org)

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Question 6: Raising Cane’s – From LSU Hangout to Chicken Juggernaut

What chicken finger purveyor began in 1996 with a single location near the campus of Louisiana State University and, by the end of 2025, had grown to nearly 1,000 locations and more than $5 billion in annual sales?

Raising Cane’s Chicken Fingers began in 1996 with one restaurant just off the North Gate of Louisiana State University in Baton Rouge; by the mid‑2020s it had expanded to over 900 locations and roughly $5.1 billion in annual system sales, ranking as the third‑largest U.S. quick‑service chicken chain behind Chick-fil-A and Popeyes.(en.wikipedia.org)

Connections

  • Origin story: Founder Todd Graves and partner Craig Silvey wrote a business plan for a chicken‑finger‑only restaurant while in college, were repeatedly rejected by lenders, then worked labor jobs to fund the first Cane’s, named after Graves’s yellow Labrador.(en.wikipedia.org)
  • Business model: Cane’s focuses on a radically simple menu—chicken fingers, fries, coleslaw, Texas toast, drinks, and a proprietary sauce—operated mostly in company-owned stores, a strategy analysts credit with helping it surpass KFC in U.S. chicken-chain sales.(en.wikipedia.org)
  • Theme-park and big-city presence: Recent expansion includes a flagship in New York’s Times Square and a first-of-its-kind location at Universal CityWalk Hollywood, bringing its minimalist menu into tourist-heavy entertainment districts.(en.wikipedia.org)
  • Pop-culture tie-ins: The chain leans into music and sports collaborations, notably Post Malone’s pink Utah Cane’s and a Dallas Cowboys–themed Cane’s in Dallas featuring his memorabilia—turning a fast-food outlet into a kind of fan shrine.(dallasnews.com)

Sources