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 A229502 Expansion of q * f(-q) * f(-q^4) * f(-q^16) * f(q, -q^3) in powers of q where f() is a Ramanujan theta function. 2
 1, 0, -2, -2, 0, 2, 2, 4, -1, -2, 0, 0, -2, -4, 2, -4, -2, 2, 6, 4, 0, 2, -6, -4, 3, 2, 0, 4, 6, 0, -8, 0, -2, 0, -4, -2, 0, -6, 2, -4, 0, 4, 0, -4, 2, 12, 8, 8, 3, -6, 4, 0, 0, -8, 2, 0, -6, -6, 0, -4, -18, 0, 2, 8, 2, 0, -10, 4, 0, 4, 10, 0, 4, 6, 0, 0, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700). LINKS G. C. Greubel, Table of n, a(n) for n = 1..2500 (terms 1..77 from Michael Somos) Eric Weisstein's World of Mathematics, Ramanujan Theta Functions FORMULA Euler transform of period 16 sequence [0, -2, -2, -1, -2, -1, 0, -4, 0, -1, -2, -1, -2, -2, 0, -4, ...]. a(2^n) = A090132(n). a(16*n + 5) = a(16*n + 11) = 0. 2 * a(n) = A229893(8*n). a(2*n) = -2 * A229893(n). EXAMPLE G.f. = q - 2*q^3 - 2*q^4 + 2*q^6 + 2*q^7 + 4*q^8 - q^9 - 2*q^10 - 2*q^13 + ... MATHEMATICA a[ n_] := SeriesCoefficient[ q QPochhammer[ q^3, -q^4] QPochhammer[ -q, -q^4] QPochhammer[ -q^4] QPochhammer[ q] QPochhammer[ q^4] QPochhammer[ q^16], {q, 0, n}]; PROG (PARI) {a(n) = my(A, m); if( n<1, 0, n--; A = x * O(x^n); polcoeff( eta(x + A) * eta(x^4 + A) * eta(x^16 + A) * sum( k=0, n, if( issquare( 8*k + 1, &m), (-1)^((m\2 + 2) \ 4) * x^k, 0), A), n))}; (Sage) CuspForms( Gamma1(16), 2, prec=78).0; (MAGMA) Basis( CuspForms( Gamma1(16), 2), 78)[1]; CROSSREFS Cf. A090132, A229893. Sequence in context: A177225 A236306 A153239 * A141661 A278521 A195910 Adjacent sequences:  A229499 A229500 A229501 * A229503 A229504 A229505 KEYWORD sign AUTHOR Michael Somos, Oct 02 2013 STATUS approved

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Last modified October 20 04:37 EDT 2019. Contains 328247 sequences. (Running on oeis4.)