This nBAB was created on the 75th anniversary of the ratification of the 21st Amendment. The 21st Amendment repealed the 18th Amendment (Prohibition).

MathBabbler Number Analyst (MBNA) output: ========================================= 21 is a natural, whole, integer 21 is odd 21 proper divisors are: 1,3,7, 21 is deficient (sum of divisors is 11) 21 is unhappy 21 is a Harshad number 21 is not prime 21 is undulating 21 has the prime factors: 3*7 21 in octal is 025 21 in hexadecimal is 0x15 21 in binary is 10101 (is odious) 21 nearest square numbers: -5...4 (16 [4]...25 [5]) sqrt(21) = 4.58258 ln(21) = 3.04452 log(21) = 1.32222 21 reciprocal is .04761904761904761904761904761904 21! is 5.10909e+19 21 is 6.68451 Pi years 21 is 1 score and 1 year

`written as a Roman numeral is`

21`.`

XXI

`is semi-prime.`

21

`[wikipedia]`

`is a Fibonacci number.`

21

`[wikipedia]`

`is the sum of the first six integers.`

21This nBAB was created in the

`st century.`

21Added the song title "

`st Century Life" to Songs With Numbers In Their Titles.`

21## Update::2013.02.21

This update was made on February

`st when Pi Day 2013 was`

21`days away. This nBAB was created in 2008 and the following is MBNA output for the number`

21`on`

21`February 2013.`

21MathBabbler Number Analyst (MBNA) output: ========================================= 21 is a natural, whole, integer 21 is odd 21 proper divisors are: 1,3,7, 21 is deficient (sum of divisors is 11) 21 is unhappy 21 is a Squarefree Number 21 is a Harshad number 21 is not prime 21 has the prime factors: 3*7 (sum=10) 21 is semiprime (biprime or 2-almost prime) 3...7...answer: 10 21 is undulating 21 is a Fibonacci number 21 is a Padovan number(12+9) 21 is a lucky number 21 is triangular 21 in octal is 025 21 in hexadecimal is 0x15 21 in binary is 10101 (is odious) 21 nearest square numbers: -5...4 (16...25 [5]) sqrt(21) = 4.58258 ln(21) = 3.04452 log(21) = 1.32222 21 reciprocal is .04761904761904761904761904761904 21! is 5.10909e+19 21 is 6.68451 Pi years 21 is 1 score and 1 year 21 written as a Roman numeral is XXI 21 = 11^2 - 10^2 and 11 + 10 = 21

**Creator:** Gerald Thurman
[gthurman@gmail.com]

**Created:** 05 December 2008

This work is licensed under a Creative Commons Attribution 3.0 United States License.