A161519 Expansion of Sum_{n >= 1} (-1)^nq^(n^2+n)(1-q^2)(1-q^4)...(1-q^(2n-2))/((1+q)(1+q^2)...(1+q^(2n))).

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

Offset

2,10

Comments

-(-1)^n*a(n) is the number of inequivalent elements of norm -n in Z[sqrt{3}].

Links

Table of n, a(n) for n=2..99.

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

Crossrefs

Sequence in context: A037858 A037876 A263774 * A286561 A068101 A094263

Adjacent sequences: A161516 A161517 A161518 * A161520 A161521 A161522

Keyword

sign

Author

Jeremy Lovejoy, Jun 12 2009

Status

approved