# The Number 21: Properties and Meanings

Prime Factors of**21**=3x7.

**21**is the third star number. Star numbers can be represented by a square with a triangle on each side. Here a 3 x 3 square is surrounded by four triangles.

**21**can be Partitioned in 792 ways.

**21**can be Partitioned 11 times with each term no larger than 2

**21**can be Partitioned 48 times with each term no larger than 3

**21**can be Partitioned 120 times with each term no larger than 4

**21**can be Partitioned 221 times with each term no larger than 5

**21**can be Partitioned 331 times with each term no larger than 6

**21**can be Partitioned 436 times with each term no larger than 7

**21**can be Partitioned 525 times with each term no larger than 8

**21**can be Partitioned 598 times with each term no larger than 9

**21**can be Partitioned 653 times with each term no larger than 10

**21**can be Partitioned 695 times with each term no larger than 11

**21**can be Partitioned 725 times with each term no larger than 12

**21**can be Partitioned 747 times with each term no larger than 13

**21**can be Partitioned 762 times with each term no larger than 14

**21**can be Partitioned 773 times with each term no larger than 15

**21**can be Partitioned 780 times with each term no larger than 16

**21**can be Partitioned 785 times with each term no larger than 17

**21**can be Partitioned 788 times with each term no larger than 18

**21**can be Partitioned 790 times with each term no larger than 19

**21**can be Partitioned 791 times with each term no larger than 20

**21**is a Triangular Number.

**21**is a Octagonal Number.

**21**is a Fibonacci Number.

**21**is a Motzkin Number.

**21**is the smallest number of distinct squares needed to tile a square.

**21**is a 2-hyperperfect number.

The numbers of binary trees of height 3=

**21**.

The Chemical Element Scandium has an atomic number of

**21**.

The

**21**divisions of the "Yama loka", for the Indians.

There are

**21**letters in the Italian alphabet.

**21**Lutetia is a large Main belt asteroid of the M spectral type.

Film:

**21**Grams.

### The Year 21 AD

In the year**21**AD Publius Sulpicius Quirinius, Roman governor of Syria, died.