OFFSET
5,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 5..1000
FORMULA
Euler transform of period 11 sequence [-5, -2, -2, -1, 1, 1, -1, -2, -2, -5, -6, ...].
EXAMPLE
G.f. = q^5 - 5*q^6 + 8*q^7 - 2*q^8 - 5*q^9 + 4*q^10 - 11*q^11 + 19*q^12 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ q^5 Product[(1 - q^k)^{5, 2, 2, 1, -1, -1, 1, 2, 2, 5, 6}[[Mod[k, 11, 1]]], {k, 1, n - 5}], {q, 0, n}];
PROG
(PARI) {a(n) = my(A); if( n<5, 0, n -= 5; A = 1 + x * O(x^n); polcoeff( prod(k=1, n, (1 - x^k)^[6, 5, 2, 2, 1, -1, -1, 1, 2, 2, 5][k%11 + 1], A), n))};
(Magma) Basis( CuspForms( Gamma1(11), 3), 69) [5];
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Mar 29 2015
STATUS
approved