54

Number
$54$ (fifty-four) is:


 * $2 \times 3^3$


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


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


 * 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.