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A153395
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G.f.: A(x) = F(x*G(x)) where F(x) = G(x/F(x)^2) = 1 + x*F(x)^2 is the g.f. of A000108 (Catalan) and G(x) = F(x*G(x)^2) = 1 + x*G(x)^4 is the g.f. of A002293.
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2
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1, 1, 3, 13, 69, 417, 2754, 19373, 142732, 1088875, 8533278, 68308641, 556242792, 4593529882, 38380159009, 323860968709, 2756019889146, 23625552635184, 203823793118268, 1768357487401595, 15418860927887232, 135042445950316514
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OFFSET
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0,3
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COMMENTS
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This appears to be the same as the sequence in row 1 of Fig. 21 of Novelli-Thibon 2014. - N. J. A. Sloane, Jun 14 2014
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LINKS
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FORMULA
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a(n) = Sum_{k=0..n} C(2k+1,k)/(2k+1) * C(4n-3k,n-k)*k/(4n-3k) for n>0 with a(0)=1.
G.f. satisfies: A(x) = 1 + x*G(x)*A(x)^2 where G(x) is the g.f. of A002293.
G.f. satisfies: A(x/F(x)^2) = F(x/F(x)) where F(x) is the g.f. of A000108.
G.f. satisfies: A(x/H(x)) = F(x) where H(x) = 1 + x*H(x)^3 is the g.f. of A001764 and F(x) is the g.f. of A000108.
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EXAMPLE
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G.f.: A(x) = F(x*G(x)) = 1 + x + 3*x^2 + 13*x^3 + 69*x^4 +... where
F(x) = 1 + x + 2*x^2 + 5*x^3 + 14*x^4 + 42*x^5 + 132*x^6 +...
F(x)^2 = 1 + 2*x + 5*x^2 + 14*x^3 + 42*x^4 + 132*x^5 + 429*x^6 +...
G(x) = 1 + x + 4*x^2 + 22*x^3 + 140*x^4 + 969*x^5 + 7084*x^6 +...
G(x)^2 = 1 + 2*x + 9*x^2 + 52*x^3 + 340*x^4 + 2394*x^5 +...
G(x)^3 = 1 + 3*x + 15*x^2 + 91*x^3 + 612*x^4 + 4389*x^5 +...
G(x)^4 = 1 + 4*x + 22*x^2 + 140*x^3 + 969*x^4 + 7084*x^5 +...
A(x)^2 = 1 + 2*x + 7*x^2 + 32*x^3 + 173*x^4 + 1050*x^5 +...
G(x)*A(x)^2 = 1 + 3*x + 13*x^2 + 69*x^3 + 417*x^4 + 2754*x^5 +...
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MATHEMATICA
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nmax = 21;
G[_] = 0;
Do[G[x_] = 1 + x*G[x]^4 + O[x]^nmax, nmax];
F[x_] = Sum[CatalanNumber[n] x^n, {n, 0, nmax}];
A[x_] = F[x G[x]];
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PROG
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(PARI) {a(n)=if(n==0, 1, sum(k=0, n, binomial(2*k+1, k)/(2*k+1)*binomial(4*(n-k)+k, n-k)*k/(4*(n-k)+k)))}
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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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