18 (number)

18 (eighteen) is the natural number following 17 and preceding 19.

In mathematics

Eighteen is a composite number, its proper divisors being 1, 2, 3, 6 and 9. It is a heptagonal number, and as the sum of the first three pentagonal numbers, it is a pentagonal pyramidal number. It is a Harshad number.

Related Topics:
Composite number - Divisor - 1 - 2 - 3 - 6 - 9 - Heptagonal number - Pentagonal number - Pentagonal pyramidal number - Harshad number

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