783

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Number

$783$ (seven hundred and eighty-three) is:

$3^3 \times 29$

The $18$th heptagonal number after $1$, $7$, $18$, $34$, $55$, $81$, $112$, $148$, $189$, $235$, $286$, $342$, $403$, $469$, $540$, $616$, $697$:

$783 = \ds \sum_{k \mathop = 1}^{18} \paren {5 k - 4} = \dfrac {18 \paren {5 \times 18 - 3} } 2$

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