840 

[World]  The ISO country code for U.S.A. (ISO-3166).

 

841

[Math.]  The 2nd square number that is the sum of squares of 2 consecutive numbers: 841 = 292 = 202+212. Each root number is 6 times the previous root number minus the earlier root number: 1, 52, 292, 1692, 9852

Or in other words:  (20, 21, 29) is the 2nd Pythagorean triple (lengths of 3 sides of a right triangle), where 2 sides are consecutive integers.

 

[Tech.]  The sides of an A0 sheet of paper, 1,189 mm×841 mm, whose area is 1 m2 (or exactly 999,949 mm2), the largest size in the “A” series for international standard office documents. The size “An” in the “A” series is 21/4–n/2 21/4–n/2 m. The side-to-side ratio of any paper is always approximately (1:21/2). A size in this “A” series can be made by folding the previous size in half, A0: 1,189×841 – A1: 841×594 – A2: 594×420– A3: 420×297A4: 297×210– A5: 210×148– A6: 148×105– A7: 105×74– A8: 74×52– A9: 52×37and A10: 37×26.

 

842

 

843

[Math.]  The 14th Lucas number.

 

844

[Phone]  An area code for the toll-free (or WATS: Wide Area Telecommunications Service) telephone number, dialing within the U.S. and Canada. Besides the original number 800, there are: 888, 877, 866 and 855 and will be 844, 833 and 822.

 

845

 

846

[Math.]  8462 = 715,716, formed by concatenation of 2 consecutive numbers.

 

847...

 

848

 

849

[Math.]  8493 = 611,960,049 = (611+960049)3.

 

840-849

[Library]  Numbers 800-899 are the first 3 digits in Dewey Decimal Classification System call numbers for library books in Literature. Numbers 840-849 are for books in French Literature.