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A186240
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G.f. A(x) defined by A(x) = 1 +x*A(x) +x^2*A(x)^2 +3*x^3*A(x)^3.
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0
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1, 1, 2, 7, 21, 66, 228, 799, 2843, 10357, 38278, 143012, 539980, 2056848, 7892496, 30483351, 118416903, 462348219, 1813410078, 7141608015, 28229040165, 111956307486, 445374729396, 1776704142348, 7105896093588, 28487216564476, 114454156300136, 460781265916312
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OFFSET
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0,3
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LINKS
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FORMULA
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a(n) = 1/n*sum(j=0..n, binomial(n,j)*sum(i=j..n+j-1, binomial(j,i-j)*binomial(n-j,3*j-n-i-1)*3^(3*j-n-i-1))), n>0
Conjecture: 6*(2*n+3)*(n+1)*a(n) +(277*n^2-191*n-162)*a(n-1) +6*(-155*n^2+305*n-126)*a(n-2) -4*(181*n-195)*(n-2)*a(n-3) -5304*(n-2)*(n-3)*a(n-4)=0. - R. J. Mathar, Sep 27 2013
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MATHEMATICA
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m = maxExponent = 20;
A[_] = 0; Do[A[x_] = 1 + x A[x] + x^2 A[x]^2 + 3 x^3 A[x]^3 + O[x]^m, {m}];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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