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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))).
0
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
Jeremy Lovejoy, Overpartitions and real quadratic fields, J. Number Theory, 106 (2004), 178-186.
CROSSREFS
Sequence in context: A298934 A309061 A289618 * A070097 A202523 A215935
KEYWORD
sign
AUTHOR
Jeremy Lovejoy, Jun 12 2009
STATUS
approved