OFFSET
1,3
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of eta(q^2)^2 * eta(q^3)^3 * eta(q^12)^3 * eta(q^18)^2 / (eta(q^4) * eta(q^6)^8 * eta(q^9)) in powers of q.
Euler transform of period 36 sequence [ 0, -2, -3, -1, 0, 3, 0, -1, -2, -2, 0, 1, 0, -2, -3, -1, 0, 2, 0, -1, -3, -2, 0, 1, 0, -2, -2, -1, 0, 3, 0, -1, -3, -2, 0, 0, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (36 t)) = f(t) where q = exp(2 Pi i t).
Convolution inverse of A058647.
EXAMPLE
G.f. = q - 2*q^3 - 3*q^4 + 6*q^6 + 8*q^7 - 14*q^9 - 18*q^10 + 30*q^12 + ...
MATHEMATICA
A233670[n_] := SeriesCoefficient[q*QPochhammer[q^2]^2*QPochhammer[q^3]^3 *QPochhammer[q^12]^3*QPochhammer[q^18]^2/(QPochhammer[q^4] * QPochhammer[q^6]^8*QPochhammer[q^9]), {q, 0, n}]; Table[A233670[n], {n, 50}] (* G. C. Greubel, Oct 09 2017 *)
PROG
(PARI) {a(n) = my(A); if( n<1, 0, n--; A = x * O(x^n); polcoeff( eta(x^2 + A)^2 * eta(x^3 + A)^3 * eta(x^12 + A)^3 * eta(x^18 + A)^2 / (eta(x^4 + A) * eta(x^6 + A)^8 * eta(x^9 + A)), n))};
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Dec 14 2013
STATUS
approved