129

Number
$129$ (one hundred and twenty-nine) is:


 * $3 \times 43$


 * The $27$th lucky number:
 * $1$, $3$, $7$, $9$, $13$, $15$, $21$, $25$, $31$, $33$, $37$, $43$, $49$, $51$, $63$, $67$, $73$, $75$, $79$, $87$, $93$, $99$, $105$, $111$, $115$, $127$, $129$, $\ldots$


 * The $23$rd happy number after $1$, $7$, $10$, $13$, $19$, $23$, $\ldots$, $91$, $94$, $97$, $100$, $103$, $109$:
 * $129 \to 1^2 + 2^2 + 9^2 = 1 + 4 + 81 = 86 \to 8^2 + 6^2 = 64 + 36 = 100 \to 1^2 + 0^2 + 0^2 = 1$


 * The $25$th positive integer $n$ such that no factorial of an integer can end with $n$ zeroes.