208,335

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Number

$208 \, 335$ is:

$3 \times 5 \times 17 \times 19 \times 43$

The $4$th and last after $1$, $55$, $91$ of the $4$ square pyramidal numbers which are also triangular.

The $85$th square pyramidal number:

$208 \, 335 = \ds \sum_{k \mathop = 1}^{85} k^2 = \dfrac {85 \paren {85 + 1} \paren {2 \times 85 + 1} } 6$

The $645$th triangular number:

$208 \, 335 = \ds \sum_{k \mathop = 1}^{645} k = \dfrac {645 \times \paren {645 + 1} } 2$

Also see

• Previous: Square Pyramidal and Triangular Numbers
• Previous  ... Next: Square Pyramidal Number
• Previous  ... Next: Triangular Number

Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $208,335$
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $208,335$