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A161516
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Expansion of 1 + 2Sum_{n >= 1} (-q)^n(1+q^2)(1+q^4)...(1+q^(2k-2))/ ((1-q)(1-q^3)...(1-q^(2n-1)))
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12
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1, -2, 0, -2, 2, 0, 2, 0, 2, -2, 2, 0, 0, -2, 0, -4, 2, 0, 0, -2, 0, -2, 2, 0, 2, -2, 2, 0, 2, 0, 2, 0, 0, -2, 2, -2, 4, 0, 0, -2, 0, 0, 0, -4, 0, -2, 2, 0, 2, -4, 0, 0, 0, -2, 2, -2, 0, 0, 2, 0, 2, -2, 0, -2, 4, 0, 4, 0, 0, 0, 0, -2, 2, 0, 0, -2, 2, 0, 4, -2
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| (-1)^na(n) is the number of inequivalent elements of norm 8n-1 in Z[sqrt{2}].
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REFERENCES
| Daniel Corson, David Favero, Kate Liesinger, Sarah Zubairy, Characters and $q$-series in ${\Bbb Q}(\sqrt{2})$, J. Number Theory, 107 (2004), 392-405.
Jeremy Lovejoy, Overpartitions and real quadratic fields, J. Number Theory, 106 (2004), 178-186.
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CROSSREFS
| Sequence in context: A088627 A024713 A123530 * A123063 A031358 A029317
Adjacent sequences: A161513 A161514 A161515 * A161517 A161518 A161519
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KEYWORD
| sign
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AUTHOR
| Jeremy Lovejoy (lovejoy(AT)liafa.jussieu.fr), Jun 12 2009
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