420

[Math.]  Two consecutive sums of consecutive numbers:  49+50+…+55+56 = 57+58+…+62+63 = 420.

 

[Sport]  The standard weight of a FIFA-approved soccer ball: 420-445 grams.

 

420 & 421

[Phone]  International telephone dialing code for Czechoslovakia. Now, 420 for Czech Republic and 421 for Slovakia.

 

420 & 422

[Sport]  The number of dimples on a golf ball usually are: 252, 286, 332, 336, 360, 384, 392, 410, 416, 420, 422, 432, 440, 480, 492 or 500. (References [6])

 

421

[Math.]  A prime number.

 

[Math.]  The (3x+1) problem: Start with any natural number. Divide it by 2 if it is even or multiply by 3 and add 1 if it is odd. The sequence will eventually end by three numbers 4, 2, 1… repeatedly.

 

422

[World]  The ISO-3166 country code for Lebanon.

 

423…

 

424

[Math.]  All 3 numbers 1,999,899, 1,999,900 and 1,999,901 have all their 404th, 414th, 424th, 434th, 444th and 454th powers starting with digits 404, 414, 424, 434, 444 and 454, respectively.

 

[Math.]  All numbers in the range [19,998,989-19,999,012] have all their 404th, 414th, 424th, 434th, 444th and 454th powers starting with digits 404, 414, 424, 434, 444 and 454, respectively.

 

[Sport]  One of soccer’s possible lineup tactics formations: 4-2-4 (4 defenders, 2 midfielders and 4 forwards). A slightly modified defenders line makes: 1-3-2-4 (1 sweeper), or 3-1-2-4 (1 stopper). A slightly modified forwards line makes: 4-2-3-1 (1 striker).

 

425

[Library]  ISBN-0-425 is the International Standard Book Number for books published by Berkley Books/Berkeley Sensation/Berkeley Publishing Group.

 

426

[World]  The ISO-3166 country code for Lesotho.

 

427…

 

428

[Math.]  A square number 4282 = 183,184, formed by concatenation of 2 consecutive numbers.

 

[World]  The ISO-3166 country code for Latvia.

 

429

[Math.]  A Catalan number: C7 = 429. 

 

420-429

[Library]  Numbers 400-499 are the first 3 digits in Dewey Decimal Classification System call numbers for library books in Languages and Linguistics. Numbers 420-429 are for books in English and Anglo-Saxon Languages.

 

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References [6]: Scientific American, I. Stewart, Mathematical Recreations, February 1997.