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 A178902 Expansion of q^(-1/24) * eta(q^2)^13 / (eta(q)^5 * eta(q^4)^5) in powers of q. 1
 1, 5, 7, 0, 0, 11, 0, -13, 0, 0, 0, 0, -17, 0, 0, -19, 0, 0, 0, 0, 0, 0, -23, 0, 0, 0, 25, 0, 0, 0, 0, 0, 0, 0, 0, 29, 0, 0, 0, 0, 31, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 35, 0, 0, 0, 0, 0, -37, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -41, 0, 0, 0, 0, 0, 0, -43, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -47, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700). LINKS Seiichi Manyama, Table of n, a(n) for n = 0..10000 G. Köhler, Some eta-identities arising from theta series, Math. Scand. 66 (1990), 147-154. Eric Weisstein's World of Mathematics, Ramanujan Theta Functions FORMULA Expansion of f(q) * phi(q)^2 = f(q)^3 * chi(q)^2 = phi(q)^3 / chi(q) in powers of q where f(), phi(), chi() are Ramanujan theta functions. Euler transform of period 4 sequence [5, -8, 5, -3, ...]. a(n) = b(24*n + 1) where b(n) is multiplicative with b(2^e) = 0^e, b(3^e) = 0^e, b(p^e) = (1 + (-1)^e)/2 * p^(e/2) if p == 1, 5, 7, 11 (mod 24), b(p^e) = (1 + (-1)^e)/2 * (-p)^(e/2) if p == 13, 17, 19, 23 (mod 24). G.f. is a period 1 Fourier series which satisfies f(-1 / (2304 t)) = 48^(3/2) (t/i)^(3/2) f(t) where q = exp(2 Pi i t). G.f.: Product_{k>0} (1 - x^(2*k))^3 * (1 + x^(2*k - 1))^5 = Sum_{k>0} Kronecker( -6, k) * k * x^((k^2 - 1) / 24) = Sum_{k in Z} (6*k + 1) * (-1)^floor(k/2) * x^(k * (3*k + 1) / 2). a(n) = (-1)^n * A080332(n). EXAMPLE G.f. = 1 + 5*x + 7*x^2 + 11*x^5 - 13*x^7 - 17*x^12 - 19*x^15 - 23*x^22 + ... G.f. = q + 5*q^25 + 7*q^49 + 11*q^121 - 13*q^169 - 17*q^289 - 19*q^361 + ... MATHEMATICA A178902[n_] := SeriesCoefficient[(QPochhammer[-q, -q]/QPochhammer[q, -q])^3/QPochhammer[-q, q^2], {q, 0, n}]; Table[A178902[n], {n, 0, 50}] (* G. C. Greubel, Aug 17 2017 *) a[ n_] := With[ {m = Sqrt[24 n + 1]}, If[ IntegerQ@m, m KroneckerSymbol[ -6, m], 0]]; (* Michael Somos, Apr 27 2018 *) a[ n_] := SeriesCoefficent[ QPochhammer[ x^2]^13 / (QPochhammer[ x] QPochhammer[ x^4]^5, {x, 0, n}]; (* Michael Somos, Apr 27 2018 *) PROG (PARI) {a(n) = if( issquare( 24*n + 1, &n), n * kronecker( -6, n), 0)}; (PARI) {a(n) = my(A, p, e); if( n<1, n==0, A = factor(24*n + 1); prod( k=1, matsize(A)[1], [p, e] = A[k, ]; if( (p<5) || (e%2), 0, if( p%24<12, p, -p)^(e\2)))))}; (PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A)^13 / (eta(x + A)^5 * eta(x^4 + A)^5), n))}; CROSSREFS Apart from signs, same as A080332, A116916, A133079 and A134756. Sequence in context: A116916 A080332 A134756 * A176713 A293506 A011350 Adjacent sequences:  A178899 A178900 A178901 * A178903 A178904 A178905 KEYWORD sign AUTHOR Michael Somos, Jun 21 2010 STATUS approved

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Last modified January 27 18:18 EST 2021. Contains 340470 sequences. (Running on oeis4.)