Composite number

A composite number is a natural number larger than 1 that is not a prime number. The first ten composite numbers are:

4, 6, 8, 9, 10, 12, 14, 15, 16 and 18.

Sphenic number

A composite number which has precisely three distinct prime factors is called a sphenic number.

The ten first sphenic numbers are:

1. 30; which is also 11-agonal by polygonality and bracketed by twin primes
2. 42; which is also a Catalan number
3. 66; which is also triangular, hexagonal, 23-agonal and a palindrome
4. 70; which is also pentagonal and 13-agonal
5. 78
6. 102; which is bracketed by twin primes
7. 105; which is also 12-agonal
8. 110
9. 114
10. 130; which is also 23-agonal

See also: Highly composite number.