A161520 Expansion of Sum_{n >= 1} q^n(1-q)(1-q^2)...(1-q^(2n-1))/((1+q^2)(1+q^4)...(1+q^(2n))).

1, 0, -1, -1, 0, 0, 0, 0, 1, 2, 0, -1, 0, 0, 0, -1, 0, 0, -2, 0, 0, 0, 0, 0, 3, 0, -1, 0, 0, 2, 0, 0, 0, 0, 0, -1, 0, 0, 0, -2, 0, 0, -2, 0, 0, 2, 0, -1, 1, 0, 0, 0, 0, 0, 0, 0, 2, 2, 0, 0, 0, 0, 0, -1, 0, 0, -2, 0, 0, 0, 0, 0, 2, 0, -3, -2, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 2, 0, 0

Offset

1,10

Comments

a(n) is -(-1)^(n(n+1)/2) times the number of inequivalent elements of norm n in Z[sqrt{6}].

Links

Table of n, a(n) for n=1..99.

Jeremy Lovejoy, Overpartitions and real quadratic fields, J. Number Theory, 106 (2004), 178-186.

Crossrefs

Sequence in context: A298934 A309061 A289618 * A070097 A202523 A215935

Adjacent sequences: A161517 A161518 A161519 * A161521 A161522 A161523

Keyword

sign

Author

Jeremy Lovejoy, Jun 12 2009

Status

approved