A218619 G.f. satisfies: A(x) = exp( Sum_{n>=1} x^n*A(x)^n/n * Sum_{k=0..2*n} A200536(n,k)^2 * x^k * A(x)^(2*k) ), where A200536(n,k) = [x^k] (1 + 3*x + 2*x^2)^n.

1, 1, 11, 72, 734, 6994, 74641, 803196, 8989482, 102192197, 1184211027, 13897707080, 165052834584, 1978844990494, 23924151189858, 291313067897212, 3569576082827250, 43981925261314302, 544590342185545146, 6772925262506494672, 84567358373934285042

Offset

0,3

Comments

More generally, given that A(x) satisfies:

A(x) = exp( Sum_{n>=1} x^n*A(x)^n/n * Sum_{k=0..2*n} TC(n,k)^2*x^k*A(x)^(2*k) ),

where TC(n,k) = [x^k] (1 + b*x + c*x^2)^n, then A(x) satisfies:

(1) A(x) = (1+x*A(x)^2)*(1+c^2*x^3*A(x)^6)*(1+(b^2-2*c)*x^2*A(x)^4+c^2*x^4*A(x)^8) / (1-2*x^2*A(x)^4)^2.

(2) A(x) = sqrt( (1/x)*Series_Reversion( x*(1-c*x^2)^4 / ((1+x)*(1+c^2*x^3)*(1+(b^2-2*c)*x^2+c^2*x^4))^2 ) ).

Links

Table of n, a(n) for n=0..20.

Formula

G.f. satisfies:

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

(2) A(x) = sqrt( (1/x)*Series_Reversion( x*(1-2*x^2)^4 / ((1+x)*(1+x^2)*(1+4*x^2)*(1+4*x^3))^2 ) ).

Example

 G.f.: A(x) = 1 + x + 11*x^2 + 72*x^3 + 734*x^4 + 6994*x^5 + 74641*x^6 +...
Let A = g.f. A(x), then the logarithm of the g.f. equals the series:
log(A(x)) = (1 + 3^2*x*A^2 + 2^2*x^2*A^4)*x*A +
(1 + 6^2*x*A^2 + 13^2*x^2*A^4 + 12^2*x^3*A^6 + 4^2*x^4*A^8)*x^2*A^2/2 +
(1 + 9^2*x*A^2 + 33^2*x^2*A^4 + 63^2*x^3*A^6 + 66^2*x^4*A^8 + 36^2*x^5*A^10 + 8^2*x^6*A^12)*x^3*A^3/3 +
(1 + 12^2*x*A^2 + 62^2*x^2*A^4 + 180^2*x^3*A^6 + 321^2*x^4*A^8 + 360^2*x^5*A^10 + 248^2*x^6*A^12 + 96^2*x^7*A^14 + 16^2*x^8*A^16)*x^4*A^4/4 +...
which involves the squares of the trinomial coefficients A200536(n,k):
1;
1, 3, 2;
1, 6, 13, 12, 4;
1, 9, 33, 63, 66, 36, 8;
1, 12, 62, 180, 321, 360, 248, 96, 16;
1, 15, 100, 390, 985, 1683, 1970, 1560, 800, 240, 32; ...

Prog

 (PARI) /* G.f. A(x) using the squares of the trinomial coefficients */
{A200536(n, k)=polcoeff((1 + 3*x + 2*x^2)^n, k)}
{a(n)=local(A=1+x); for(i=1, n, A=exp(sum(m=1, n, sum(k=0, 2*m, A200536(m, k)^2*x^k*(A+x*O(x^n))^(2*k))*x^m*A^m/m))); polcoeff(A, n)}
for(n=0, 30, print1(a(n), ", "))
(PARI) {a(n)=local(A=sqrt(serreverse( x*(1-2*x^2)^4/((1+x)*(1+x^2)*(1+4*x^2)*(1+4*x^3+x*O(x^n)))^2 )/x)); polcoeff(A, n)}
for(n=0, 30, print1(a(n), ", "))

Crossrefs

Cf. A200536, A200537, A218298.

Sequence in context: A260585 A084900 A300968 * A197308 A142015 A123039

Adjacent sequences: A218616 A218617 A218618 * A218620 A218621 A218622

Keyword

nonn

Author

Paul D. Hanna, Nov 03 2012

Status

approved