S = n = 1 ∑ ∞ n 4 d ( n ) n = 1 ∑ ∞ n 4 2 ω ( n )
Where ω ( n ) counts the number of distinct prime factors of n , and d ( n ) is the number of divisors of n .
S = b π c a enter your answer as a + b + c
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In the solution are you using the fact that omega is a multiplicative function.
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For any prime p we have n = 0 ∑ ∞ p n s 2 ω ( p n ) = 1 + n = 1 ∑ ∞ p n s 2 = 1 + 1 − p − s 2 p − s = 1 − p − s 1 + p − s for s > 1 , and hence n = 1 ∑ ∞ n s 2 ω ( n ) = p ∏ 1 − p − s 1 + p − s = ζ ( s ) × ζ ( 2 s ) ζ ( s ) = ζ ( 2 s ) ζ ( s ) 2 for s > 1 , while n = 1 ∑ ∞ n s d ( n ) = ζ ( s ) 2 for s > 1 , so that S s = ζ ( 2 s ) 1 s > 1 With s = 4 we obtain S 4 = ζ ( 8 ) − 1 = π 8 9 4 5 0 , making the answer 9 4 5 0 + 1 + 8 = 9 4 5 9 .