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Problem #271

GCD Fun

Let f(x_1, x_2, x_3 … x_n) = x_1 * x_2 * ...x_n * (2^{gcd(x_1, x_2, … x_n)}). Let S_n be the sum of f(x_1, x_2, x_3 … x_n) over all sequences (x_1, x_2, x_3 … x_n) where 1 <= x_i <= 10^6. Find S_{31415} modulo 10^9 + 7.

gcd

Contributed by Kalptaru Agarwal

Solved by 11 users

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