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A096963
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a(n) = Sum {0<d|n, n/d odd} d^11.
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8
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1, 2048, 177148, 4194304, 48828126, 362799104, 1977326744, 8589934592, 31381236757, 100000002048, 285311670612, 743012564992, 1792160394038, 4049565171712, 8649804864648, 17592186044416, 34271896307634
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OFFSET
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1,2
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COMMENTS
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This is the member k=11 of the k-family sigma^#_k(n) := Sum {0<d|n, n/d odd} d^k.
This notation appears in the Ono et al. link, Theorem 5 (with k=3, see A007331) and Theorem 8 (with k=11). - Wolfdieter Lang, Jan 13 2017
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LINKS
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FORMULA
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G.f.: Sum_{n>0} n^11 * x^n / (1 - x^(2*n)).
a(n) = Sum {0<d|n, n/d odd} d^11.
Multiplicative with a(2^e) = 2^(11*e) and a(p^e) = (p^(11*e+11)-1)/(p^11-1) for p > 2.
Sum_{k=1..n} a(k) ~ c * n^12, where c = 1365*zeta(12)/16384 = 691*Pi^12/7664025600 = 0.0833334904... . (End)
Dirichlet g.f.: zeta(s)*zeta(s-11)*(1-1/2^s). - Amiram Eldar, Jan 09 2023
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EXAMPLE
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G.f. = q + 2048*q^2 + 177148*q^3 + 4194304*q^4 + 48828126*q^5 + ...
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MATHEMATICA
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a[ n_] := If[ n < 1, 0, Sum[ d^11 Boole[ OddQ[ n/d]], {d, Divisors[ n]}]]; (* Michael Somos, Nov 30 2014 *)
a[ n_] := SeriesCoefficient[ With[{u1 = QPochhammer[ q]^8, u4 = QPochhammer[ q^4]^8}, q (u1^4 + 2072 q u4 u1^3 + 210048 q^2 u4^2 u1^2 + 5660672 q^3 u4^3 u1 + 45285376 q^4 u4^4) / u1 ], {q, 0, n}]; (* Michael Somos, Nov 30 2014 *)
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PROG
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(PARI) {a(n) = if( n<1, 0, sumdiv( n, d, (n/d%2) * d^11))}; /* Michael Somos, Nov 30 2014 */
(Sage) ModularForms( Gamma0(2), 12, prec=18).3; # Michael Somos, Nov 30 2014
(Magma) A := Basis( ModularForms( Gamma0(2), 12), 18); A[2] + 2048*A[3] + 177148*A[4]; /* Michael Somos, Nov 30 2014 */
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CROSSREFS
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KEYWORD
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nonn,mult
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AUTHOR
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STATUS
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approved
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