A161219 a(n) = (1/n) * Sum_{d|n} phi(n/d)*2^(d+1).
4, 6, 8, 12, 16, 28, 40, 72, 120, 216, 376, 704, 1264, 2364, 4384, 8232, 15424, 29204, 55192, 104976, 199760, 381492, 729448, 1398504, 2684368, 5162856, 9942136, 19175160, 37025584, 71585136, 138547336, 268439592, 520602352, 1010588256, 1963413664, 3817763800
Offset: 1
Keywords
Links
- Andrew Howroyd, Table of n, a(n) for n = 1..1000
Programs
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PARI
a(n) = sumdiv(n, d, eulerphi(n/d)*2^(d+1))/n; \\ Michel Marcus, Apr 15 2021
Formula
G.f.: -2 * Sum_{k>=1} phi(k) * log(1 - 2*x^k) / k. - Ilya Gutkovskiy, Apr 15 2021
a(n) = 2*A000031(n). - Hugo Pfoertner, Jun 24 2021