1525

Number
$1525$ (one thousand, five hundred and twenty-five) is:
 * $5^2 \times 61$


 * The $25$th heptagonal number after $1, 7, 18, 34, 55, 81, 112, \ldots, 874, 970, 1071, 1177, 1288, 1404$:
 * $1525 = \displaystyle \sum_{k \mathop = 1}^{25} \left({5 k - 4}\right) = \dfrac {25 \left({5 \times 25 - 3}\right)} 2$