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1, 1, 2, 6, 16, 52, 172, 586, 2048, 7286, 26216, 95326, 349536, 1290556, 4793492, 17895736, 67108864, 252645136, 954437292, 3616814566, 13743895360, 52357696956, 199911205052, 764877654106, 2932031008768, 11258999068468, 43303842570872, 166799986203766, 643371375338656, 2484744621997516
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,3
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LINKS
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FORMULA
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a(n) = (1/(4*n)) * Sum_{odd d divides n} phi(d)*4^(n/d) for n > 0.
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MATHEMATICA
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a[n_] := DivisorSum[n, EulerPhi[#] * 4^(n/#) &, OddQ[#] &] / (4*n); a[0] = 1; Array[a, 30, 0] (* Amiram Eldar, Oct 04 2023 *)
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PROG
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(PARI) a(n) = if (n==0, 1, sumdiv(n, d, if (d % 2, eulerphi(d)*4^(n/d)))/(4*n)); \\ Michel Marcus, Mar 11 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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