Are you smarter than me? 13

(Find\ { (19 }^{ 92 })mod(92)


The answer is 49.

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2 solutions

Aneesh Kundu
Dec 4, 2014

Since gcd ( 19 , 92 ) = 1 \gcd(19,92)=1 and ϕ ( 92 ) = 44 \phi(92)=44

By Euler-Fermat theorem we have 1 9 44 1 m o d 92 19^{44}\equiv 1 \mod 92 1 9 88 1 m o d 92 \Rightarrow 19^{88}\equiv 1\mod 92 1 9 92 1 9 4 36 1 2 ( 7 ) 2 m o d 92 \Rightarrow 19^{92}\equiv 19^{4}\equiv 361^2\equiv (-7)^2\mod 92 1 9 92 49 m o d 92 \boxed{19^{92}\equiv 49\mod 92}

Brian Brooks
Dec 4, 2014

Built-in Python:

pow(19, 92, 92)

Memory-efficient method utilizing "(a x b) mod m == (a x (b mod m)) mod m":

def pow2(b, e, m):
    c = 1
    i = 0
    while i < e:
        i = i + 1
        c = (c * b) % m
    return c

print pow2(19, 92, 92)

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