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A132211
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Coefficients of a Ramanujan q-series.
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1
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1, -1, 0, 0, 0, 0, -1, 1, -1, 1, -1, 2, -2, 2, -2, 2, -2, 2, -2, 2, -2, 2, -1, 1, -1, 0, 1, -1, 1, -2, 3, -4, 4, -5, 7, -8, 8, -9, 11, -12, 12, -13, 15, -16, 16, -17, 19, -20, 19, -20, 22, -22, 21, -21, 22, -22, 20, -19, 20, -19, 16, -14, 14, -12, 8, -5, 3, 0, -5, 10, -13, 17, -24, 30, -34, 40, -48, 55, -61, 68, -77, 86, -93, 101
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,12
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FORMULA
| G.f.: Sum_{k>=0} (-1)^k* q^(k*(k+1)/2)/ (q^2;q^2)_n.
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EXAMPLE
| 1 - q - q^6 + q^7 - q^8 + q^9 - q^10 + 2*q^11 - 2*q^12 + 2*q^13 - ...
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PROG
| (PARI) {a(n)= local(t); if(n<0, 0, t= 1 +x*O(x^n); polcoeff( sum(k=1, (sqrtint(8*n+1)-1)\2, t= -t* x^k/ (1-x^(2*k)) +x*O(x^n), 1), n))}
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CROSSREFS
| Sequence in context: A160093 A035931 A140438 * A067441 A044926 A074264
Adjacent sequences: A132208 A132209 A132210 * A132212 A132213 A132214
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KEYWORD
| sign
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AUTHOR
| Michael Somos, Aug 13 2007
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