OFFSET
0,37
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
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, 0, 0, 1, 1, 1, 1, 0, 0, -1, -1, -2, -1, -1, 0, 0, 1, 1, 1, 1, 0, 0, -1, -1, ...].
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
KEYWORD
sign
AUTHOR
Michael Somos, Jan 20 2012
STATUS
approved