6545

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Number

$6545$ (six thousand, five hundred and forty-five) is:

$5 \times 7 \times 11 \times 17$

The $33$rd tetrahedral number, after $1$, $4$, $10$, $20$, $35$, $\ldots$, $3276$, $3276$, $4060$, $4495$, $4960$, $5456$, $5984$:

$6545 = \ds \sum_{k \mathop = 1}^{33} \frac {k \paren {k + 1} } 2 = \dfrac {33 \paren {33 + 1} \paren {33 + 2} } 6$

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