Numeric Value: 21

The folowing table expresses '21' in various number bases. 'DRx' shows the result of 'digit reducing' resulting in an X-digit long number.

BaseDR5DR4DR3DR2DR1
210101  11,101
3  210101
4  111 3
5   41,101
6   33,101
7   303
8   257
9   235
10   213
11   1A,101
12   19A
13   189
14   178
15   167
16   156

Math World

Factors: 3 * 7

21 is the 8th Fibonacci number.

21 is in the Pythagorean Triples: (21, 220, 221), (20, 21, 29).

21 is the sum of the counting numbers from 1 to 6 (See 'The Sum/Product of the First N Counting Numbers').

Physical World

21 is the atomic weight of Scandium (Sc).