345

Number
$345$ (three hundred and forty-five) is:


 * $3 \times 5 \times 23$


 * The $15$th second pentagonal number after $2, 7, 15, 26, 40, 57, 77, 100, 126, 155, 187, 222, 260, 301$:
 * $345 = \dfrac {15 \left({3 \times 15 + 1}\right)} 2$


 * The $19$th number after $1, 3, 22, 66, 70, 81, 94, 115, 119, 170, 210, 214, 217, 265, 282, 310, 322, 343$ whose $\sigma$ value is square: