3553

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Number

$3553$ (three thousand, five hundred and fifty-three) is:

$11 \times 17 \times 19$

The $38$th heptagonal number after $1$, $7$, $18$, $34$, $55$, $81$, $112$, $\ldots$, $2205$, $2356$, $2512$, $2673$, $2839$, $3010$, $3186$, $3367$:

$3553 = \ds \sum_{k \mathop = 1}^{38} \paren {5 k - 4} = \dfrac {38 \paren {5 \times 38 - 3} } 2$

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