A104527 Denominator of sum(1/(phi(k)sigma(k)),k=1..n), where phi(k) is the totient function and sigma(k) is the sum of the divisors function.
1, 3, 24, 168, 7, 168, 112, 1680, 21840, 65520, 65520, 16380, 32760, 21840, 29120, 902720, 8124480, 8124480, 1624896, 1624896, 3249792, 5416320, 59579520, 59579520, 59579520, 178738560, 178738560, 178738560, 178738560, 178738560
Offset: 1
Examples
a(3)=24 because phi(1)*sigma(1)+phi(2)*sigma(2)+phi(3)*sigma(3)=1/(1*1)+1/(1*3)+1/(2*4)=35/24.
Programs
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Maple
with(numtheory): a:=n->denom(sum(1/phi(k)/sigma(k),k=1..n)): seq(a(n),n=1..35);
Comments