781

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Number

$781$ (seven hundred and eighty-one) is:

$11 \times 71$

The $5$th Fermat pseudoprime to base $5$ after $4$, $124$, $217$, $561$:

$5^{781} \equiv 5 \pmod {781}$

The $6$th of the $3$-digit integers $m$ which need the largest number of reverse-and-add process iterations ($23$) before reaching a palindromic number:

$781$, $968$, $1837$, $\ldots$, $8713200023178$

Also see

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• Previous  ... Next: 3-Digit Numbers forming Longest Reverse-and-Add Sequence