Voozh

A246464

G.f. satisfies: A(x) = Sum_{n>=0} x^n * A(x)^n / (1-x)^(2*n+1) * [ Sum_{k=0..n} C(n,k)^2 * x^k ]^2.

1, 2, 9, 51, 327, 2252, 16259, 121406, 929743, 7261742, 57620811, 463174907, 3763666589, 30864808636, 255117429497, 2123195981867, 17776511724391, 149625900208462, 1265371478104067, 10746502200129133, 91616252419847037, 783751482672817832, 6725892179235421461

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,2

LINKS

Paul D. Hanna, Table of n, a(n) for n = 0..100

FORMULA

G.f. satisfies:

(1) A(x) = Sum_{n>=0} x^n / (1 - x*A(x))^(2*n+1) * [ Sum_{k=0..n} C(n,k)^2 * x^k * A(x)^k ]^2.

(2) A(x) = Sum_{n>=0} x^n * Sum_{k=0..n} C(n,k)^2 * A(x)^k * Sum_{j=0..k} C(k,j)^2 * x^j.

(3) A(x) = Sum_{n>=0} x^n * Sum_{k=0..n} C(n,k)^2 * A(x)^(n-k) * Sum_{j=0..k} C(k,j)^2 * x^j * A(x)^j.

(4) A(x) = Sum_{n>=0} x^n * A(x)^n * Sum_{k>=0} A143007(n,k) * x^k.

(5) A(x) = Sum_{n>=0} x^n * Sum_{k=0..n} A143007(n-k,k) * A(x)^k.

a(n) ~ c * d^n / n^(3/2), where d = 9.17670192065271..., c = 0.488111443264... . - Vaclav Kotesovec, Aug 27 2014

EXAMPLE

G.f.: A(x) = 1 + 2*x + 9*x^2 + 51*x^3 + 327*x^4 + 2252*x^5 + 16259*x^6 +...

where A = g.f. A(x) is given by the binomial series identity:

A(x) = 1/(1-x) + x*A(x)/(1-x)^3 * (1 + x)^2

+ x^2*A^2/(1-x)^5 * (1 + 2^2*x + x^2)^2

+ x^3*A^3/(1-x)^7 * (1 + 3^2*x + 3^2*x^2 + x^3)^2

+ x^4*A^4/(1-x)^9 * (1 + 4^2*x + 6^2*x^2 + 4^2*x^3 + x^4)^2

+ x^5*A^5/(1-x)^11 * (1 + 5^2*x + 10^2*x^2 + 10^2*x^3 + 5^2*x^4 + x^5)^2 +...

equals the series

A(x) = 1/(1-x*A) + x/(1-x*A)^3 * (1 + x*A)^2

+ x^2/(1-x*A)^5 * (1 + 2^2*x*A + x^2*A^2)^2

+ x^3/(1-x*A)^7 * (1 + 3^2*x*A + 3^2*x^2*A^2 + x^3*A^3)^2

+ x^4/(1-x*A)^9 * (1 + 4^2*x*A + 6^2*x^2*A^2 + 4^2*x^3*A^3 + x^4*A^4)^2

+ x^5/(1-x*A)^11 * (1 + 5^2*x*A + 10^2*x^2*A^2 + 10^2*x^3*A^3 + 5^2*x^4*A^4 + x^5*A^5)^2 +...

We can also express the g.f. by another binomial series identity:

A(x) = 1 + x*(1 + A*(1+x)) + x^2*(1 + 2^2*A*(1+x) + A^2*(1+2^2*x+x^2))

+ x^3*(1 + 3^2*A*(1+x) + 3^2*A^2*(1+2^2*x+x^2) + A^3*(1+3^2*x+3^2*x^2+x^3))

+ x^4*(1 + 4^2*A*(1+x) + 6^2*A^2*(1+2^2*x+x^2) + 4^2*A^3*(1+3^2*x+3^2*x^2+x^3) + A^4*(1+4^2*x+6^2*x^2+4^2*x^3+x^4))

+ x^5*(1 + 5^2*A*(1+x) + 10^2*A^2*(1+2^2*x+x^2) + 10^2*A^3*(1+3^2*x+3^2*x^2+x^3) + 5^2*A^4*(1+4^2*x+6^2*x^2+4^2*x^3+x^4) + A^5*(1+5^2*x+10^2*x^2+10^2*x^3+5^2*x^4+x^5)) +...

equals the series

A(x) = 1 + x*(A + (1+x*A)) + x^2*(A^2 + 2^2*A*(1+x*A) + (1+2^2*x*A+x^2*A^2))

+ x^3*(A^3 + 3^2*A^2*(1+x*A) + 3^2*A*(1+2^2*x*A+x^2*A^2) + (1+3^2*x*A+3^2*x^2*A^2+x^3*A^3))

+ x^4*(A^4 + 4^2*A^3*(1+x*A) + 6^2*A^2*(1+2^2*x*A+x^2*A^2) + 4^2*A*(1+3^2*x*A+3^2*x^2*A^2+x^3*A^3) + (1+4^2*x*A+6^2*x^2*A^2+4^2*x^3*A^3+x^4*A^4))

+ x^5*(A^5 + 5^2*A^4*(1+x*A) + 10^2*A^3*(1+2^2*x*A+x^2*A^2) + 10^2*A^2*(1+3^2*x*A+3^2*x^2*A^2+x^3*A^3) + 5^2*A*(1+4^2*x*A+6^2*x^2*A^2+4^2*x^3*A^3+x^4*A^4) + (1+5^2*x*A+10^2*x^2*A^2+10^2*x^3*A^3+5^2*x^4*A^4+x^5*A^5)) +...

More explicitly, the g.f. can be written as the series:

A(x) = (1 + x + x^2 + x^3 + x^4 + x^5 + x^6 +...)

+ x*A(x)*(1 + 5*x + 13*x^2 + 25*x^3 + 41*x^4 + 61*x^5 +...)

+ x^2*A(x)^2*(1 + 13*x + 73*x^2 + 253*x^3 + 661*x^4 + 1441*x^5 +...)

+ x^3*A(x)^3*(1 + 25*x + 253*x^2 + 1445*x^3 + 5741*x^4 +...)

+ x^4*A(x)^4*(1 + 41*x + 661*x^2 + 5741*x^3 + 33001*x^4 +...)

+ x^5*A(x)^5*(1 + 61*x + 1441*x^2 + 17861*x^3 + 142001*x^4 +...) +...

where the coefficients form the square array A143007.

PROG

(PARI) /* By definition: */

{a(n)=local(A=1+x); for(i=1, n, A=sum(m=0, n, x^m * A^m / (1-x +x*O(x^n))^(2*m+1) * sum(k=0, m, binomial(m, k)^2*x^k)^2 )); polcoeff(A, n)}