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A239051
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Expansion of (f(-q^2, -q^3)^5 - 3 * q * f(-q, -q^4)^5) / f(-q)^3 in powers of q where f() is a Ramanujan theta function.
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1
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1, 0, 10, -10, 10, 0, 0, 10, 0, -10, 10, 0, 10, -10, 20, -10, 0, 10, -10, 0, 10, 0, 20, -10, 0, 0, 0, 0, 10, 0, 0, 0, 10, -20, 20, 10, 0, 10, 0, -20, 0, 0, 20, -10, 20, -10, 0, 10, -10, 10, 10, 0, 10, -10, 0, 0, 0, 0, 0, 0, 10, 0, 20, -10, 10, -10, 0, 10, 10
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OFFSET
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0,3
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COMMENTS
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LINKS
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FORMULA
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Moebius transform is period 5 sequence [ 0, 10, -10, 0, 0, ...].
G.f.: 1 + 10 * ( Sum_{k>=0} x^(5*k + 2) / (1 - x^(5*k + 2)) - x^(5*k + 3) / (1 - x^(5*k + 3)) ).
a(5*n) = a(n). a(5*n + 1) = 0.
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EXAMPLE
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G.f. = 1 + 10*q^2 - 10*q^3 + 10*q^4 + 10*q^7 - 10*q^9 + 10*q^10 + 10*q^12 + ...
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MATHEMATICA
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a[ n_] := If[ n < 1, Boole[ n == 0], 10 Sum[ {0, 1, -1, 0, 0}[[ Mod[ d, 5, 1] ]] ], {d, Divisors @ n}]];
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PROG
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(PARI) {a(n) = if( n<1, n==0, 10 * sumdiv(n, d, (d%5==2) - (d%5==3)))};
(Sage) ModularForms( Gamma1(5), 1, prec=70).0;
(Magma) Basis( ModularForms( Gamma1(5), 1), 70) [1];
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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