70

Number
$70$ (seventy) is:


 * $2 \times 5 \times 7$


 * The $7$th pentagonal number after $1, 5, 12, 22, 35, 51$:
 * $70 = 1 + 4 + 7 + 10 + 13 + 16 + 19 = \dfrac {7 \left({3 \times 7 - 1}\right)} 2$


 * The $\sigma$ value of $70$ is square: