OFFSET
1,7
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) * eta(q^3) * eta(q^5) * eta(q^12) * eta(q^20) * eta(q^30) / (eta(q^6) * eta(q^10))^3 in powers of q.
Euler transform of a period 60 sequence.
G.f. is a period 1 Fourier series which satisfies f(-1 / (60 t)) = f(t) where q = exp(2 Pi i t).
EXAMPLE
G.f. = q - q^3 - q^4 - q^5 + 2*q^7 + 2*q^8 - q^9 - 2*q^10 + q^12 + 2*q^13 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ q QPochhammer[ q^2] QPochhammer[ q^30] / (QPochhammer[ -q^3] QPochhammer[ -q^5]), {q, 0, n}]; (* Michael Somos, Sep 06 2015 *)
PROG
(PARI) {a(n) = my(A); if( n<1, 0, n--; A = x * O(x^n); polcoeff( eta(x^2 + A) * eta(x^3 + A) * eta(x^5 + A) * eta(x^12 + A) * eta(x^20 + A) * eta(x^30 + A) / (eta(x^6 + A) * eta(x^10 + A))^3, n))};
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Oct 23 2008
STATUS
approved