A204843 - OEIS

A204843

Expansion of x * f(-x^24) + (3 * phi(-x^36) - phi(-x^4)) / 2 in powers of x where phi(), f() are Ramanujan theta functions.

1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0

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OFFSET

0,37

COMMENTS

Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700).

LINKS

Antti Karttunen, Table of n, a(n) for n = 0..65537

Michael Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

FORMULA

Expansion of phi(-x^36) + x * f(-x^24) + x^4 * f(-x^12, -x^60) in powers of x where phi(), f() are Ramanujan theta functions.

Expansion of f(-x^9, x^9) + x * f(x^3, -x^15) in powers of x where f() is the two variable Ramanujan theta function.

Euler transform of period 24 sequence [ 1, -1, 0, 1, -1, 1, -1, 0, 0, 0, 1, -2, 1, 0, 0, 0, -1, 1, -1, 1, 0, -1, 1, -1, ...].

a(3*n + 2) = a(4*n + 2) = a(4*n + 3) = a(5*n + 2) = a(5*n + 3) = a(6*n + 3) = a(8*n + 5) = 0. a(4*n) = A089810(n). a(24*n + 1) = A010815(n). a(25*n) = a(49*n) = A204853(n).

EXAMPLE

1 + x + x^4 - x^16 - x^25 - 2*x^36 - x^49 - x^64 + x^100 + x^121 + ...

MATHEMATICA

a[n_]:= SeriesCoefficient[(3*EllipticTheta[3, 0, -q^36] -EllipticTheta[3, 0, -q^4])/2 + q*QPochhammer[q^24, q^72]*QPochhammer[q^48, q^72]* QPochhammer[q^72, q^72], {q, 0, n}]; Table[a[n], {n, 0, 100}] (* G. C. Greubel, Dec 19 2017 *)

PROG

(PARI) {a(n) = local(m); if( n<1, n==0, if( issquare( n, &m), (-1)^(m\6) * [ 2, 1, 1, 0, -1, -1][m%6 + 1]))}

CROSSREFS

Cf. A089810, A010815, A204853.

Sequence in context: A091888 A083928 A074038 * A204853 A303709 A185778

Adjacent sequences: A204840 A204841 A204842 * A204844 A204845 A204846

KEYWORD

sign

AUTHOR

Michael Somos, Jan 19 2012

STATUS

approved