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.