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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified August 18 13:46 EDT 2019. Contains 326100 sequences. (Running on oeis4.)