640

[Measure]  The number of acres in a square mile.

U.S. customary units for area measures: 1 acre = 160 square rods = 4,840 square yards = 43,560 square feet = 6,272,640 square inches = 4046.8564224 m2 & 1 square mile (1 section) = 640 acres = 2,589,988.11 m2 = 2.59 km2 = 259 hectares & 1 hectare = 2.471 acres = 10,000 m2 & 1 township = 36 square miles. 

 

641

[Math.]  A prime number.

 

[Math.]  A prime factor of the smallest composite Fermat number:

(1+2^(25)) = 1+232 = 4,294,967,297 = 641´6700417.

 

642 

[World]  The ISO country code for Romania. (ISO-3166)

 

643

[Math.]  A prime number.

123,456 = 643×64×3.

 

[World]  The ISO country code for Russia. (ISO-3166)

 

644

 

645

[Math.]  1+2+…+645 = 12+22+…+852 = 208,335.

 

646  

[World]  The ISO country code for Rwanda. (ISO-3166)

 

647

[Math.]  A prime number.

 

648

[Math.]  648 = 12×23×34.

 

[Math.]  6483 = 272,097,792 = (–27–20–97+792)3.

 

649

[Phone]  The telephone area code for Turks and Caicos Islands (within U.S./NANPA).


640-649

[Library]  Numbers 600-699 are the first 3 digits in Dewey Decimal Classification System call numbers for library books in Applied Sciences and Technology (Medicine, Agriculture and Engineering…). Numbers 640-649 are for books in Home Economics and Family Living.