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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))).
0
-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
Jeremy Lovejoy, Overpartitions and real quadratic fields, J. Number Theory, 106 (2004), 178-186.
CROSSREFS
Sequence in context: A037858 A037876 A263774 * A286561 A068101 A094263
KEYWORD
sign
AUTHOR
Jeremy Lovejoy, Jun 12 2009
STATUS
approved