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 A128711 Expansion of phi(x) * psi(x^4) * phi(-x^4)^4 in powers of x where phi(), psi() are Ramanujan theta functions. 3
 1, 2, 0, 0, -5, -14, 0, 0, 2, 34, 0, 0, 25, -28, 0, 0, -28, 0, 0, 0, -46, -14, 0, 0, 49, 4, 0, 0, 68, 82, 0, 0, 0, -62, 0, 0, -142, 50, 0, 0, -11, -158, 0, 0, 146, 0, 0, 0, -94, 70, 0, 0, 0, 178, 0, 0, 98, 0, 0, 0, 75, -92, 0, 0, -28, -62, 0, 0, -238, -206, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Number 48 of the 74 eta-quotients listed in Table I of Martin (1996). Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700). - Michael Somos, Mar 14 2012 LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 Y. Martin, Multiplicative eta-quotients, Trans. Amer. Math. Soc. 348 (1996), no. 12, 4825-4856, see page 4852 Table I. Michael Somos, Index to Yves Martin's list of 74 multiplicative eta-quotients and their A-numbers Michael Somos, Introduction to Ramanujan theta functions Eric Weisstein's World of Mathematics, Ramanujan Theta Functions FORMULA Expansion of q^(-1/2) * (eta(q^2) * eta(q^4))^5 / (eta(q) * eta(q^8))^2 in powers of q. - Michael Somos, Mar 14 2012 Euler transform of period 8 sequence [ 2, -3, 2, -8, 2, -3, 2, -6, ...]. a(n) = b(2*n + 1) where b() is multiplicative with b(2^e) = 0^e, b(p^e) = (1 + (-1)^e)/2 * p^e if p == 5, 7 (mod 8), b(p^e) = b(p) * b(p^(e-1)) - p^2 * b(p^(e-2)) if p == 1, 3 (mod 8) where b(p) = 2*(2*x^2 - p) * (-1)^((p-1)/2) and p = x^2 + 2*y^2. G.f. is a period 1 Fourier series which satisfies f(-1 / (32 t)) = 2^(15/2) (t/i)^3 f(t) where q = exp(2 Pi i t). G.f.: Product_{k>0} (1 - x^k)^6 * (1 + x^k)^8 * (1 + x^(2*k))^3 / (1 + x^(4*k))^2. a(4*n + 2) = a(4*n + 3) = 0. a(4*n) = A128712(n). a(4*n + 1) = 2 * A128713(n). EXAMPLE G.f. = 1 + 2*x - 5*x^4 - 14*x^5 + 2*x^8 + 34*x^9 + 25*x^12 - 28*x^13 + ... G.f. = q + 2*q^3 - 5*q^9 - 14*q^11 + 2*q^17 + 34*q^19 + 25*q^25 - 28*q^27 + ... MATHEMATICA a[ n_] := SeriesCoefficient[ (QPochhammer[ x^2] QPochhammer[ x^4])^5 / (QPochhammer[ x] QPochhammer[ x^8])^2, {x, 0, n}]; (* Michael Somos, Jul 09 2015 *) PROG (PARI) {a(n) = my(A, p, e, x, y, a0, a1); if( n<0, 0, n = 2*n + 1; A = factor(n); prod( k=1, matsize(A)[1], [p, e] = A[k, ]; if( p==2, 0, p%8>4, if( e%2, 0, p^e), for( i=1, sqrtint(p\2), if( issquare(p - 2*i^2, &x), break)); a0=1; a1=y=2*(2*x^2 - p) * (-1)^((p-1)/2); for( i=2, e, x = y*a1 - p^2*a0; a0=a1; a1=x); a1)))}; (PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( (eta(x^2 + A) * eta(x^4 + A))^5 / (eta(x + A) * eta(x^8 + A))^2, n))}; CROSSREFS Cf. A128712, A128713. Sequence in context: A281190 A275619 A249132 * A132710 A106512 A181229 Adjacent sequences: A128708 A128709 A128710 * A128712 A128713 A128714 KEYWORD sign AUTHOR Michael Somos, Mar 24 2007 STATUS approved

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