OFFSET
0,4
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
Masao Koike, Modular forms on non-compact arithmetic triangle groups, Unpublished manuscript [Extensively annotated with OEIS A-numbers by N. J. A. Sloane, Feb 14 2021. I wrote 2005 on the first page but the internal evidence suggests 1997.]
FORMULA
Expansion of (c(q) / 3)^6 in powers of q where c() is a cubic AGM theta function. - Michael Somos, Jun 07 2012
Expansion of (eta(q^3)^3 / eta(q))^6 in powers of q.
G.f.: (Product_{k>0} (1 - x^(3*k))^3 / (1 - x^k))^6. - Michael Somos, Jun 07 2012
Convolution square of A106402. - Michael Somos, Dec 26 2015
EXAMPLE
G.f. = q^2 + 6*q^3 + 27*q^4 + 80*q^5 + 207*q^6 + 432*q^7 + 863*q^8 + 1512*q^9 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ q^2 (QPochhammer[ q^3]^3 / QPochhammer[ q])^6, {q, 0, n}]; (* Michael Somos, Feb 22 2015 *)
PROG
(PARI) {a(n) = my(A); if( n<2, 0, n -= 2; A = x * O(x^n); polcoeff( (eta(x^3 + A)^3 / eta(x + A))^6, n))}; /* Michael Somos, Jun 07 2012 */
(Magma) A := Basis( ModularForms( Gamma1(3), 6), 36); A[3]; /* Michael Somos, Feb 22 2015 */
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 01 2011
STATUS
approved