3078
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Number
$3078$ (three thousand and seventy-eight) is:
- $2 \times 3^4 \times 19$
- The $18$th pentagonal pyramidal number after $1$, $6$, $12$, $40$, $75$, $126$, $196$, $288$, $405$, $550$, $726$, $936$, $1183$, $1470$, $1800$, $2176$, $2601$:
- $3078 = \ds \sum_{k \mathop = 1}^{18} \dfrac {k \paren {3 k - 1} } 2 = \dfrac {18^2 \paren {18 + 1} } 2$