9880
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Number
$9880$ (nine thousand, eight hundred and eighty) is:
- $2^3 \times 5 \times 13 \times 19$
- The $38$th tetrahedral number, after $1$, $4$, $10$, $20$, $35$, $\ldots$, $3276$, $3276$, $4060$, $4495$, $4960$, $5456$, $5984$, $6545$, $7140$, $7770$, $8436$, $9139$:
- $9880 = \ds \sum_{k \mathop = 1}^{38} \frac {k \paren {k + 1} } 2 = \dfrac {38 \paren {38 + 1} \paren {38 + 2} } 6$