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Search: id:A124243
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| A124243 |
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Expansion of q*psi(q^9)/psi(q) in powers of q. |
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+0
4
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| 1, -1, 1, -2, 3, -4, 5, -7, 10, -12, 15, -20, 26, -32, 39, -50, 63, -76, 92, -114, 140, -168, 201, -244, 295, -350, 415, -496, 591, -696, 818, -967, 1140, -1332, 1554, -1820, 2126, -2468, 2861, -3324, 3855, -4448, 5126, -5916, 6816, -7824, 8970, -10292, 11793, -13471, 15372, -17548
(list; graph; listen)
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OFFSET
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1,4
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FORMULA
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Expansion of eta(q)/eta(q^9)*(eta(q^18)/eta(q^2))^2 in powers of q.
Euler transform of period 18 sequence [ -1, 1, -1, 1, -1, 1, -1, 1, 0, 1, -1, 1, -1, 1, -1, 1, -1, 0, ...].
G.f. A(x) satisfies 0=f(A(x), A(x^2)) where f(u, v)= u^2 -v +v*(2*u -3*u^2 +v).
G.f.: x*Product_{k>0} (1-x^k)*(1-x^(18k))^2/((1-x^(2k))^2*(1-x^(9k))).
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PROGRAM
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(PARI) {a(n)=local(A); if(n<1, 0, n--; A=x*O(x^n); polcoeff( eta(x+A)*eta(x^18+A)^2/eta(x^2+A)^2/eta(x^9+A), n))}
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CROSSREFS
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Sequence in context: A022957 A036028 A036033 this_sequence A132975 A145977 A050729
Adjacent sequences: A124240 A124241 A124242 this_sequence A124244 A124245 A124246
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KEYWORD
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sign
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AUTHOR
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Michael Somos, Oct 28 2006
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