1525

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Number

$1525$ (one thousand, five hundred and twenty-five) is:

$5^2 \times 61$

The $25$th heptagonal number after $1$, $7$, $18$, $34$, $55$, $81$, $112$, $\ldots$, $874$, $970$, $1071$, $1177$, $1288$, $1404$:

$1525 = \ds \sum_{k \mathop = 1}^{25} \paren {5 k - 4} = \dfrac {25 \paren {5 \times 25 - 3} } 2$

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