Số học, Úc 2018

Đề bài: Find all pairs of positive integers (n,k) such that $n!+8=2^k$.
Notice: $1!=1,2!=2,3!=6,4!=24,5!=120,6!=720=16*45$
$\implies n\ge 6$ is not possible
n=1 -   Not Okie
n=2 -   Not Okie
n=3 -   Not Okie
n=4 -   Okie -> k=5
n= 5 - Okie -> k=7

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