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
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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