OFFSET
0,6
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..10000
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
a(n) = A282892(2n).
Expansion of (f(x^3, x^5) - 1) / f(-x, -x^2) in powers of x where f(, ) is Ramanujan's general theta function. - Michael Somos, Feb 24 2017
EXAMPLE
G.f. = x^3 + x^4 + 3*x^5 + 4*x^6 + 7*x^7 + 10*x^8 + 16*x^9 + 22*x^10 + 33*x^11 + ...
MAPLE
with(numtheory):
b:= proc(n, t) option remember; `if`(n=0, 1, add(add(`if`(
(d+t)::odd, d, 0), d=divisors(j))*b(n-j, t), j=1..n)/n)
end:
a:= n-> b(2*n, 0) -b(2*n, 1):
seq(a(n), n=0..80); # Alois P. Heinz, Feb 24 2017
MATHEMATICA
f[n_] := Length[ IntegerPartitions[n, All, 2Range[n] -1]] - Length[ IntegerPartitions[n, All, 2 Range[n]]]; Array[ f[2#] &, 52]
a[ n_] := SeriesCoefficient[ Sum[ Sign @ SquaresR[1, 16 k + 1] x^k, {k, n}] / QPochhammer[x], {x, 0, n}]; (* Michael Somos, Feb 24 2017 *)
PROG
(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( sum(k=1, n, issquare(16*k + 1)*x^k, A) / eta(x + A), n))}; /* Michael Somos, Feb 24 2017 */
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Feb 24 2017
STATUS
approved