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A192619
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G.f. satisfies: A(x) = Product_{n>=1} (1 + x^n*A(x)^(1/2))^2/(1 - x^n*A(x)^(1/2))^2.
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1
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1, 4, 20, 104, 556, 3048, 17064, 97216, 562036, 3289836, 19461448, 116178600, 699045176, 4235292680, 25816944176, 158223753376, 974389668364, 6026623271840, 37420762694588, 233179517592232, 1457706542138344, 9139698522931008
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OFFSET
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0,2
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LINKS
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FORMULA
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EXAMPLE
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G.f.: A(x) = 1 + 4*x + 20*x^2 + 104*x^3 + 556*x^4 + 3048*x^5 +...
The g.f. A = A(x) satisfies:
A = (1+x*A^(1/2))^2/(1-x*A^(1/2))^2 * (1+x^2*A^(1/2))^2/(1-x^2*A^(1/2))^2 * (1+x^3*A^(1/2))^2/(1-x^3*A^(1/2))^2 *...
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PROG
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(PARI) {a(n)=local(A=1+x); for(i=1, n, A=prod(m=1, n, (1+x^m*A^(1/2))^2/(1-x^m*A^(1/2)+x*O(x^n))^2)); polcoeff(A, n)}
(PARI) {a(n)=local(A=1+x); for(i=1, n, A=(1+sum(m=1, n, x^m*A^(m/2)*prod(k=1, m, (1+x^(k-1))/(1-x^k+x*O(x^n)))))^2); polcoeff(A, n)}
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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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