OFFSET
0,11
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 eta(q) * eta(q^12)^3 / (eta(q^4) * eta(q^6) * eta(q^9) * eta(q^18)) in powers of q.
Euler transform of period 36 sequence [ -1, -1, -1, 0, -1, 0, -1, 0, 0, -1, -1, -2, -1, -1, -1, 0, -1, 2, -1, 0, -1, -1, -1, -2, -1, -1, 0, 0, -1, 0, -1, 0, -1, -1, -1, 0, ...].
a(3*n) = 0 unless n=0. a(3*n + 1) = a(6*n + 2) = -A092848(n).
EXAMPLE
1 - q - q^2 + q^4 + q^8 - 2*q^10 + 2*q^13 + q^16 - 4*q^19 - 2*q^20 + ...
MATHEMATICA
eta[x_] := x^(1/24)*QPochhammer[x]; A182035[n_] := SeriesCoefficient[ eta[q]*eta[q^12]^3/(eta[q^4]*eta[q^6]*eta[q^9]*eta[q^18] ), {q, 0, n}];
Table[A182035[n], {n, 0, 50}] (* G. C. Greubel, Aug 21 2017 *)
PROG
(PARI) {a(n) = local(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x + A) * eta(x^12 + A)^3 / (eta(x^4 + A) * eta(x^6 + A) * eta(x^9 + A) * eta(x^18 + A)), n))}
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Apr 07 2012
STATUS
approved