54

Number
$54$ (fifty-four) is:


 * $2 \times 3^3$


 * The $12$th semiperfect number after $6, 12, 18, 20, 24, 28, 30, 36, 40, 42, 48$:
 * $54 = 9 + 18 + 27$


 * The $2$nd integer solution to $\sigma \left({n}\right) = \sigma \left({n + 2}\right)$ after $33$:
 * $\sigma \left({54}\right) = 120 = \sigma \left({56}\right)$


 * The $10$th positive integer $n$ after $5, 11, 17, 23, 29, 30, 36, 42, 48$ such that no factorial of an integer can end with $n$ zeroes.


 * The $32$nd positive integer after $2$, $3$, $4$, $7$, $8$, $\ldots$, $33$, $37$, $38$, $42$, $43$, $44$, $45$, $46$, $49$, $50$ which cannot be expressed as the sum of distinct pentagonal numbers.