671

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Number

$671$ (six hundred and seventy-one) is:

$11 \times 61$

The $3$rd integer after $3$, $228$ whose square is the sum of $2$ coprime cubes:

$671^2 = 65^3 + 56^3$

The $4$th Fermat pseudoprime to base $3$ after $91$, $121$, $286$:

$3^{671} \equiv 3 \pmod {671}$

The magic constant of a magic square of order $11$, after $1$, $(5)$, $15$, $34$, $65$, $111$, $175$, $260$, $369$, $505$:

$671 = \ds \dfrac 1 {11} \sum_{k \mathop = 1}^{11^2} k = \dfrac {11 \paren {11^2 + 1} } 2$

Also see

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• Previous  ... Next: Fermat Pseudoprime to Base 3
• Previous  ... Next: Magic Constant of Magic Square