2356

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Number

$2356$ (two thousand, three hundred and fifty-six) is:

$2^2 \times 19 \times 31$

The $31$st heptagonal number after $1$, $7$, $18$, $34$, $55$, $81$, $112$, $\ldots$, $1525$, $1651$, $1782$, $1918$, $2059$, $2205$:

$2356 = \ds \sum_{k \mathop = 1}^{31} \paren {5 k - 4} = \dfrac {31 \paren {5 \times 31 - 3} } 2$

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