115

Number
$115$ (one hundred and fifteen) is:


 * $5 \times 23$


 * The $5$th heptagonal pyramidal number after $1, 8, 26, 60$:
 * $115 = 1 + 7 + 18 + 34 + 55 = \dfrac {5 \left({5 + 1}\right) \left({5 \times 5 - 2}\right)} 6$


 * The $36$th semiprime:
 * $115 = 5 \times 23$


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


 * The index (after $2, 3, 6, 30, 75, 81$) of the $7$th Woodall prime:
 * $115 \times 2^{115} - 1$


 * The $8$th number after $1, 3, 22, 66, 70, 81, 94$ whose $\sigma$ value is square:


 * The $1$st term of the $2$nd $5$-tuple of consecutive integers have the property that they are not values of the $\sigma$ function $\sigma \left({n}\right)$ for any $n$:
 * $\left({115, 116, 117, 118, 119}\right)$