690

[Math.]  The denominator of the 44th Bernoulli number.

 

[Phone]  International telephone dialing code for Tokelau.

 

[Tech.]  The “number system” code of an EAN-13 barcode for China’s products: 690, 691 and 692.

 

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

 

690, 691 & 692

[Tech.]  The “number system” code of an EAN-13 barcode for China’s products: 690, 691 and 692.

 

691

[Library]  ISBN-0-691 is the International Standard Book Number for books published by Princeton University Press.

 

[Math.]  A prime number.

 

[Math.]  The numerator of the 12th Bernoulli number: B12 = 691/2730.

 

[Math.]  The infinite sum Sn(1/n12) = pi12×691/638512875 = z(12), where Sn is the infinite sum which n runs over all positive integers and z(s) is the Riemann zeta function over complex variable s.

 

[Math.]  The Ramanujan “tau” function t(n) is divisible by 691 for almost all positive integers n. Conjectured by Ramanujan, proved by G. N. Watson.

 

[Phone]  International telephone dialing code for Federated States of Micronesia.

 

692

[Phone]  International telephone dialing code for Marshall Islands.

 

693

[Math.]  6934 = 230,639,102,001 = (23+0639+10+20+01)4.

 

[Math.]  A primitive Pythagorean triangle of sides (693, 1924, 2045) has area 666,666.

 

694 

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

 

695

 

696

[Calendar]  The number of hours in February of a leap year.

 

696 & 697

[Math.]  The 4th square number that is the sum of squares of 2 consecutive numbers: 970,225 = 9852 = 6962+6972. The nth root number is 6 times the (n–1)th root minus the (n–2)th root: 1, 52, 292, 1692, 9852

Or in other words:

(696, 697, 985) is the 4th Pythagorean triple (lengths of 3 sides of a right triangle), where 2 sides are consecutive integers.

 

697

[Tech.]  The Dual Tone Multi-Frequency (DTMF) Keypad 

Frequency

1209 Hz

1336 Hz

1477 Hz

1633 Hz

697 Hz

1

2

3

A

770 Hz

4

5

6

B

852 Hz

7

8

9

C

941 Hz

*

0

#

D

 

698

 

699...

 

680-689

[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 690-699 are for books in Buildings.