3240

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Number

$3240$ (three thousand, two hundred and forty) is:

$2^3 \times 3^4 \times 5$

The $80$th triangular number after $1$, $3$, $6$, $10$, $15$, $\ldots$, $2701$, $2775$, $2850$, $2926$, $3003$, $3081$, $3160$:

$3240 = \ds \sum_{k \mathop = 1}^{80} k = \dfrac {80 \times \paren {80 + 1} } 2$

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