3081

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Number

$3081$ (three thousand and eighty-one) is:

$3 \times 13 \times 79$

The $78$th triangular number after $1$, $3$, $6$, $10$, $15$, $\ldots$, $2211$, $2278$, $2346$, $2415$, $2485$, $2556$, $2628$, $2701$, $2775$, $2850$, $2926$, $3003$:

$3081 = \ds \sum_{k \mathop = 1}^{78} k = \dfrac {78 \times \paren {78 + 1} } 2$

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