# 12

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## Number

$12$ (twelve) is:

$2^2 \times 3$

The base of the duodecimal number system

The number of edges of the regular octahedron and its dual, the cube

The number of distinct pentominoes, up to reflection

The $1$st power of $12$ after the zeroth $1$:
$12 = 12^1$

The $1$st of three $2$-digit integers divisible by both the sum and product of its digits:
$12 = \paren {1 + 2} \times 4 = \paren {1 \times 2} \times 6$

The $1$st abundant number:
$1 + 2 + 3 + 4 + 6 = 16 > 12$

The $2$nd semiperfect number after $6$:
$12 = 2 + 4 + 6$

The $3$rd pentagonal number after $1$, $5$:
$12 = 1 + 4 + 7 = \dfrac {3 \paren {3 \times 3 - 1} } 2$

The $3$rd superfactorial after $1$, $2$: