124

Number
$124$ (one hundred and twenty-four) is:


 * $2^2 \times 31$


 * The $2$nd Fermat pseudoprime to base $5$ after $4$:
 * $5^{124} \equiv 5 \pmod {124}$


 * The $3$rd even integer that cannot be expressed as the sum of $2$ prime numbers of which the smaller one is $3$, $5$ or $7$.


 * The $7$th untouchable number after $2$, $5$, $52$, $88$, $96$, $120$.


 * The $17$th nontotient after $14$, $26$, $34$, $38$, $50$, $62$, $68$, $74$, $76$, $86$, $90$, $94$, $98$, $114$, $118$, $122$:
 * $\nexists m \in \Z_{>0}: \map \phi m = 124$
 * where $\map \phi m$ denotes the Euler $\phi$ function


 * The $55$th positive integer after $2$, $3$, $4$, $7$, $8$, $\ldots$, $95$, $96$, $100$, $101$, $102$, $107$, $112$, $116$ which cannot be expressed as the sum of distinct pentagonal numbers.