15,251

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Number

$15 \, 251$ (fifteen thousand, two hundred and fifty-one) is:

$101 \times 151$

The $6$th pentagonal number after $1$, $5$, $22$, $1001$, $2882$ which is also palindromic:

$15 \, 251 = \ds \sum_{k \mathop = 1}^{101} \paren {3 k - 2} = \dfrac {101 \paren {3 \times 101 - 1} } 2$

Also see

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