2,100

[Calendar]  This year is a non-leap year, following the adoption of the current Gregorian calendar, created by Pope Gregory XIII in 1582 to reform the old Julian calendar.

 

[Calendar]  The last year of the 21st century.

 

2,101

[Calendar]  The first year of the 22nd century.

 

2,109

[Math.]  A pyramidal number (sum of all squares of integers from 1 to 18): 2109 = 12+22+…+172+182.

 

2,111

[Math.]  A prime number. 

21112 = 4,456,321 and 1,236,544 = 11122. 

 

2,131

[Math.]  A prime number. 

 

[Money]  A JCB credit card number starts with either 2131 or 1800 (15-digit card) or 3 (for 16-digit card).

 

2,141

[Math.]  A prime number.   Professor Umbugio’s famous “The End of the World” formula: the number 1492n–1770n–1863n+2141n is divisible by 1946, for all values of n up to 1945, where 1492, 1770, 1863 are the year of the Discovery of the New World by Christopher Columbus, the Boston Massacre and the Gettysburg Address, respectively. (E. Starke, Professor Umbugio’s prediction, American Mathematical Monthly, 54, January 1947.)

 

2,145

[Math.]  A triangular number (sum of all integers from 1 to 65): 2145 = 1+2+…+64+65.

 

2,147

[Math.]  21472 = 4,609,609.

 

2,149

[Money]  An enRoute credit card number starts with either 2014 or 2149.

 

2,160

[Math.]  Sum (in degrees) of all internal angles of a 14-side polygon.

 

2,163

[Math.]  The number of Carmichael numbers less than 25,000,000,000.

 

2,164

[Math.]  21647 = 222,229,032,256,296,835,170,304.

 

2,170

[History]  The length (miles) of the Oregon Trail, the longest of the overland routes used (between 1841 and 1867) in the westward expansion of the U.S., connecting Missouri, Kansas, Iowa, Nebraska, Wyoming, Idaho, Oregon (ending at Oregon City) and Washington (Fort Vancouver).

 

2,178

[Math.] 

(*)   8712 = 2178×4 & 8712×2178 = 18,974,736 = 43562 (= 664).

87128712 = 21782178×4 & 87128712×21782178 = 435643562

 

(**)   87912 = 21978×4 & 21978×87912 = 1,932,129,936 = 439562

8791287912 = 21978…21978×4 & 21978…21978×87912…87912 = 43956…439562

 

(***)   879912 = 219978×4 & 219978×879912 = 193,561,281,936 = 4399562

879912879912 = 219978219978×4 &

219978219978×879912879912 = 4399564399562

 

(****)   879…912 = 219…978×4 & 219…978×879…912 = 439…9562

879…912…879…912 = 219…978…219…978×4 &

                         219...978...219...978×879...912...879...912 = 439...956...439...9562.


2,197

[Math.]  133 = 2197 = 53+73+93+103 = 13+53+63+73+83+103.