65

Number
$65$ (sixty-five) is:


 * $5 \times 13$


 * The $23$rd semiprime:
 * $65 = 5 \times 13$


 * The $5$th octagonal number, after $1, 8, 21, 40$:
 * $65 = 1 + 7 + 13 + 19 + 25 = 5 \left({3 \times 5 - 2}\right)$


 * The $8$th integer after $7, 13, 19, 35, 38, 41, 57$ the decimal representation of whose square can be split into two parts which are each themselves square:
 * $65^2 = 4225; 4 = 2^2, 225 = 15^2$