We have as 31 prime using Wilsons theorem
$30! + 1 \equiv 0 \pmod {31}$
or $30 * 29! + 1 \equiv 0 \pmod {31}$
as $30 \equiv - 1 \pmod {31}$
so we have $-1 * 29! + 1 \equiv 0 \pmod {31}$
Or $ 29! -1 \equiv 0 \pmod {31}$
Or $ 4 * 29! - 4 \equiv 0 \pmod {31}$
adding 124 which is multiple of 31 we get
$ 4 * 29! + 120 \equiv 0 \pmod {31}$
or $ 4 * 29! + 5! \equiv 0 \pmod {31}$
Proved
No comments:
Post a Comment