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A074352
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Coefficient of q^1 in nu(n), where nu(0)=1, nu(1)=b and, for n>=2, nu(n)=b*nu(n-1)+lambda*(1+q+q^2+...+q^(n-2))*nu(n-2) with (b,lambda)=(1,2).
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12
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0, 0, 0, 2, 8, 22, 60, 146, 352, 814, 1860, 4170, 9256, 20326, 44300, 95874, 206320, 441758, 941780, 2000058, 4233144, 8932310, 18796700, 39457522, 82643328, 172743182, 360399460, 750625066, 1560902472, 3241109574, 6720828460, 13918875490, 28792188176
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OFFSET
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0,4
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COMMENTS
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Coefficient of q^0 is A001045(n+1).
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LINKS
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FORMULA
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a(0) = 0 for n>0, a(n) = (1/27)*(2^n*(6*n-11) + (-1)^n*(6*n-16)).
G.f.: 2*x^3*(1 + 2*x) / ((1 + x)^2*(1 - 2*x)^2).
a(n) = 2*a(n-1) + 3*a(n-2) - 4*a(n-3) - 4*a(n-4) for n>4.
(End)
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EXAMPLE
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The first 6 nu polynomials are nu(0)=1, nu(1)=1, nu(2)=3, nu(3)=5+2q, nu(4)=11+8q+6q^2, nu(5)=21+22q+20q^2+14q^3+4q^4, so the coefficients of q^1 are 0,0,0,2,8,22.
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PROG
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(PARI) a(n)=if(n<1, 0, (1/27)*(2^n*(6*n-11)+(-1)^n*(6*n-16)))
(PARI) a(n)=if(n<1, 0, (1/81)*(2^(n-1)*(6*n^2-43)+ (-1)^n*(6*n^2-24*n+62)))
(PARI) concat(vector(3), Vec(2*x^3*(1 + 2*x) / ((1 + x)^2*(1 - 2*x)^2) + O(x^40))) \\ Colin Barker, Nov 18 2017
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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Y. Kelly Itakura (yitkr(AT)mta.ca), Aug 21 2002
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EXTENSIONS
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STATUS
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approved
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