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A103258
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G.f. = theta_4(0,x^4)/theta_4(0,x).
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3
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1, 2, 4, 8, 12, 20, 32, 48, 72, 106, 152, 216, 304, 420, 576, 784, 1056, 1412, 1876, 2472, 3240, 4224, 5472, 7056, 9056, 11566, 14712, 18640, 23520, 29572, 37056, 46272, 57600, 71488, 88456, 109152, 134332, 164884, 201888, 246608, 300528, 365428, 443392, 536856
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OFFSET
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0,2
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COMMENTS
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G.f. for the number of partitions of 2n in which all odd parts occur with multiplicities 2, 4 or 6. The even parts appear at most three times. E.g., a(8)=12 because 8 = 6+2 = 6+1+1 = 4+4 = 4+2+2 = 4+2+1+1 = 4+1+1+1+1 = 3+3+2 = 3+3+1+1 = 2+2+2+1+1 = 2+2+1+1+1+1 = 2+1+1+1+1+1+1.
Also the number of partitions of 2n in which the even parts appear with 2 types c, c* and with multiplicity 1. The odd parts with multiplicity 4. E.g., a(6)=8 because we have 6, 6*, 42, 42*, 4*2, 4*2*, 21111, 2*1111.
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LINKS
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FORMULA
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Expansion of eta(q^2)*eta(q^4)^2/(eta(q)^2*eta(q^8)) in powers of q.
Euler transform of period 8 sequence [2, 1, 2, -1, 2, 1, 2, 0, ...]. - Michael Somos, Feb 10 2005
G.f.: product_{k>0} ((1+x^k)^2 * (1+x^(2*(2*k-1)))).
a(n) ~ sqrt(3)*Pi * BesselI(1, sqrt(3*n)*Pi/2) / (8*sqrt(n)).
a(n) ~ 3^(1/4) * exp(Pi*sqrt(3*n)/2) / (8*n^(3/4)) * (1 - sqrt(3)/(4*Pi*sqrt(n)) - 5/(32*Pi^2*n)).
(End)
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MATHEMATICA
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nmax = 60; CoefficientList[Series[Product[(1-x^(4*k)) * (1-x^(8*k-4)) * (1+x^k) / (1-x^k), {k, 1, nmax}], {x, 0, nmax}], x]
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PROG
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(PARI) {a(n)=local(A); if(n<0, 0, A=x*O(x^n); polcoeff( eta(x^2+A)*eta(x^4+A)^2/eta(x+A)^2/eta(x^8+A), n))} /* Michael Somos, Feb 10 2005 */
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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