Numbers 21,000s

A page of the Numeropedia - the Special Encyclopedia of Numbers

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21,120

[Geology]  The length (feet) of the Chesapeake Bay Bridge, connecting Sandy Point to Stevensville, Maryland, opened in 1952. The longest suspension bridge in the U.S.

21,222

[Zip]  U.S. Postal Zip Code: Dundalk, Maryland 21222.

21,240

[Math.]  Sum (in degrees) of all internal angles of a 120-side polygon.

21,252

[Calendar]  Imaginary rhythms have 23-day “physical” cycles, 28-day “emotional” cycles and 33-day “intellectual” cycles. The complete rhythm cycle is 21,252 days (over 58 years).

21,397

[Math.]  A prime number.  213972 = 457,831,609, a square using all 9 digits 0-9 once, except digit 2.

213nn

[Zip]  No such U.S. Postal Zip Codes.

21,439

[Math.]  214392 = 459,630,721, a square using all 9 digits 0-9 once, except digit 8.

21,600

[Math.]  21,600 = 25×33×52.

[Math.]  Sum (in degrees) of all internal angles of a 122-side polygon.

21,658

[Math.]  The equality 3094×7 = 21,658 uses each of 10 digits 0-9 once.

21,701

[Math.]  A prime number. A Mersenne exponent: 221701–1 is the 25th Mersenne prime number.

21,735

[Math.]  Two multiples of number 4347, 4347×2 = 8694 and 4347×5 = 21,735, use each of 9 digits 1-9 once.

21,744

[Math.]  217442 = 472,801,536, one of 22 squares using all 9 digits 0-8 once.

21,801

[Math.]  218012 = 475,283,601, one of 22 squares using all 9 digits 0-8 once.

21,843

[Math.]  Two multiples of number 7281, 7281×3 = 21,843 and 7281×7 = 50,967, use each of 10 digits 0-9 once.

21,845

[Math.]  A regular polygon with this odd number (product of Fermat prime numbers) of sides is constructible by using only straightedge and compass. 21845 = 5´17´257.

21,877

[Math.]  218772 = 478,603,129, a square using all 9 digits 0-9 once, except digit 5.

21,901

[Math.]  219012 = 479,653,801, a square using all 9 digits 0-9 once, except digit 2.

21,904

[Math.]  Three square numbers using the same digits: 1482 = 21904, 2032 = 41209 and 3022 = 91204.

21,948

[Math.]  21,948,126,201 = (21948+126,201)2 = 148,1492 and 725,650,126,201 = (725650+126201)2 = 851,8512 and 149,149+851851 = 1,000,000.

21,952

[Math.]  283 = 21,952 = (2+19+5+2)3.

21,978

[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…43956

(***)   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 &

21nnn

[Zip]  U.S. Postal Zip Codes of Maryland: 21nnn and 206nn-209nn.