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A216447
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G.f. satisfies: A(x) = (1 + x*(1-x)*A(x)^2) * (1 + x^2*A(x)^2).
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3
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1, 1, 2, 6, 19, 64, 228, 841, 3181, 12277, 48156, 191400, 769168, 3120044, 12758080, 52533265, 217637308, 906511243, 3793989118, 15947205096, 67290484581, 284934164506, 1210374907352, 5156562941596, 22027291990432, 94325712634264, 404842107811880
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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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G.f. A(x) satisfies:
(1) A(x) = exp( Sum_{n>=1} x^n*A(x)^n/n * Sum_{k=0..n} binomial(n,k)^2 * x^k*(1-x)^(n-k) ).
(2) A(x) = exp( Sum_{n>=1} L(n)*x^n/n ) where L(n) = [x^n] ((1-x^4)/(1-x-x^3))^n.
(3) A(x) = (1/x) * Series_Reversion( x*(1-x-x^3)/(1-x^4) ).
(4) A(x) = (1 - x^4*A(x)^4) / (1 - x*A(x) - x^3*A(x)^3).
(5) A( x*(1-x-x^3)/(1-x^4) ) = (1-x^4)/(1-x-x^3).
a(n) = [x^n] ((1-x^4)/(1-x-x^3))^(n+1) / (n+1).
Recurrence: 31*(n-1)*n*(n+1)*(877*n^4 - 9157*n^3 + 32799*n^2 - 48009*n + 24592)*a(n) = 2*(n-1)*n*(95593*n^5 - 1032316*n^4 + 3953542*n^3 - 6623680*n^2 + 4768887*n - 1162262)*a(n-1) - (n-1)*(402543*n^6 - 4844150*n^5 + 22130482*n^4 - 48931238*n^3 + 54934501*n^2 - 29672070*n + 6219456)*a(n-2) + 4*(143828*n^7 - 2089338*n^6 + 12282478*n^5 - 37816765*n^4 + 65573867*n^3 - 63612965*n^2 + 31782331*n - 6379188)*a(n-3) - 16*(n-3)*(49112*n^6 - 639080*n^5 + 3201244*n^4 - 7806610*n^3 + 9609821*n^2 - 5589051*n + 1241722)*a(n-4) + 64*(n-4)*(n-3)*(10524*n^5 - 108130*n^4 + 387266*n^3 - 581563*n^2 + 354497*n - 75516)*a(n-5) - 256*(n-5)*(n-4)*(n-3)*(877*n^4 - 5649*n^3 + 10590*n^2 - 6374*n + 1102)*a(n-6). - Vaclav Kotesovec, Aug 18 2013
a(n) ~ c*d^n/n^(3/2), where d=4.54477579... is the root of the equation -256 + 512*d - 384*d^2 + 272*d^3 - 187*d^4 + 31*d^5 = 0 and c = 0.448853665050529472948816... - Vaclav Kotesovec, Aug 18 2013
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EXAMPLE
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G.f.: A(x) = 1 + x + 2*x^2 + 6*x^3 + 19*x^4 + 64*x^5 + 228*x^6 + 841*x^7 +...
The logarithm of the g.f. begins:
log(A(x)) = ((1-x) + x)*x*A(x) + ((1-x)^2 + 2^2*x*(1-x) + x^2)*x^2*A(x)^2/2 +
((1-x)^3 + 3^2*x*(1-x)^2 + 3^2*x^2*(1-x) + x^3)*x^3*A(x)^3/3 +
((1-x)^4 + 4^2*x*(1-x)^3 + 6^2*x^2*(1-x)^2 + 4^2*x^3*(1-x) + x^4)*x^4*A(x)^4/4 +
((1-x)^5 + 5^2*x*(1-x)^4 + 10^2*x^2*(1-x)^3 + 10^2*x^3*(1-x)^2 + 5^2*x^4*(1-x) + x^5)*x^5*A(x)^5/5 +...
Explicitly,
log(A(x)) = x + 3*x^2/2 + 13*x^3/3 + 51*x^4/4 + 206*x^5/5 + 861*x^6/6 + 3641*x^7/7 + 15523*x^8/8 + 66676*x^9/9 +...+ L(n)*x^n/n +...
where L(n) = [x^n] ((1-x^4)/(1-x-x^3))^n.
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MATHEMATICA
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nmax=20; aa=ConstantArray[0, nmax]; aa[[1]]=1; Do[AGF=1+Sum[aa[[n]]*x^n, {n, 1, j-1}]+koef*x^j; sol=Solve[Coefficient[(1+x*(1-x)*AGF^2)*(1+x^2*AGF^2)-AGF, x, j]==0, koef][[1]]; aa[[j]]=koef/.sol[[1]], {j, 2, nmax}]; Flatten[{1, aa}] (* Vaclav Kotesovec, Aug 18 2013 *)
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PROG
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(PARI) {a(n)=local(A=1+x); for(i=1, n, A=(1 + x*(1-x)*A^2)*(1+x^2*A^2) +x*O(x^n)); polcoeff(A, n)}
(PARI) {a(n)=local(A=1+x); for(i=1, n, A=exp(sum(m=1, n+1, x^m*A^m/m*sum(k=0, m, binomial(m, k)^2*x^k*(1-x)^(m-k) +x*O(x^n))))); polcoeff(A, n)}
(PARI) {a(n)=polcoeff(((1-x^4)/(1-x-x^3 +x*O(x^n)))^(n+1)/(n+1), n)}
(PARI) {a(n)=polcoeff((1/x)*serreverse(x*(1-x-x^3)/(1-x^4 +x^2*O(x^n))), n)}
for(n=0, 40, print1(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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