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.