5566

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Number

$5566$ (five thousand, five hundred and fifty-six) is:

$2 \times 11^2 \times 23$

The $22$nd pentagonal pyramidal number after $1$, $6$, $12$, $40$, $75$, $\ldots$, $1470$, $1800$, $2176$, $2601$, $3078$, $3610$, $4200$, $4851$:

$5566 = \ds \sum_{k \mathop = 1}^{22} \dfrac {k \paren {3 k - 1} } 2 = \dfrac {22^2 \paren {22 + 1} } 2$

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