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A088717 G.f. satisfies: A(x) = 1 + x*A(x)^2*A(x*A(x)^2). 12
1, 1, 3, 14, 84, 596, 4785, 42349, 406287, 4176971, 45640572, 526788153, 6392402793, 81247489335, 1078331283648, 14907041720241, 214187010762831, 3192620516380376, 49287883925072010, 786925082232918304, 12976244331714379149, 220728563512663520510 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..21.

FORMULA

a(n) = coefficient of x^n in (1+x*A(x))^(2*n+1)/(2*n+1) where A(x) = Sum_{n=0} a(n)*x^n.

Recurrence:

Let A(x)^m = Sum_{n>=0} a(n,m)*x^n with a(0,m)=1, then

a(n,m) = Sum_{k=0..n} m*C(2n+m,k)/(2n+m) * a(n-k,k). [Paul D. Hanna, Dec 16 2010]

G.f. A(x) = F(x,1) where F(x,n) satisfies: F(x,n) = F(x,n-1)*(1 + x*F(x,n)*F(x,n+1)) for n>0 with F(x,0)=1. - Paul D. Hanna, Apr 16 2007

EXAMPLE

G.f.: A(x) = 1 + x + 3*x^2 + 14*x^3 + 84*x^4 + 596*x^5 + 4785*x^6 +...

G.f. A(x) is the unique solution to variable A in the infinite system of simultaneous equations:

A = 1 + x*A*B;

B = A*(1 + x*B*C);

C = B*(1 + x*C*D);

D = C*(1 + x*D*E);

E = D*(1 + x*E*F); ...

where B(x) = A(x)*A(x*A(x)^2), C(x) = A(x)*B(x*A(x)^2),  D(x) = A(x)*C(x*A(x)^2), ...

Expansions of a few of the functions described above begin:

B(x) = 1 + 2*x + 9*x^2 + 55*x^3 + 402*x^4 + 3328*x^5 + 30312*x^6 +...

C(x) = 1 + 3*x + 18*x^2 + 138*x^3 + 1218*x^4 + 11856*x^5 + 124467*x^6 +...

D(x) = 1 + 4*x + 30*x^2 + 278*x^3 + 2901*x^4 + 32846*x^5 + 395913*x^6 +...

ALTERNATE GENERATING METHOD.

Suppose functions A=A(x), B=B(x), C=C(x), etc., satisfy:

A = 1 + x*A^2*B,

B = 1 + x*(A*B)^2*C,

C = 1 + x*(A*B*C)^2*D,

D = 1 + x*(A*B*C*D)^2*E, etc.,

then B(x) = A(x*A(x)^2), C(x) = B(x*A(x)^2), D(x) = C(x*A(x)^2), etc.,

where A(x) = 1 + x*A(x)^2*A(x*A(x)^2) is the g.f. of this sequence.

Expansions of a few of the functions described above begin:

B(x) = 1 + x + 5*x^2 + 33*x^3 + 256*x^4 + 2223*x^5 + 21058*x^6 +...

C(x) = 1 + x + 7*x^2 + 60*x^3 + 578*x^4 + 6045*x^5 + 67421*x^6 +...

D(x) = 1 + x + 9*x^2 + 95*x^3 + 1098*x^4 + 13526*x^5 + 175176*x^6 +...

MATHEMATICA

m = 22; A[_] = 0; Do[A[x_] = 1 + x A[x]^2 A[x A[x]^2] + O[x]^m, {m}];

CoefficientList[A[x], x] (* Jean-Fran├žois Alcover, Nov 07 2019 *)

PROG

(PARI) {a(n)=local(A=1+x); for(i=0, n, A=1+x*A^2*subst(A, x, x*A^2+x*O(x^n))); polcoeff(A, n)}

(PARI) /* a(n) = [x^n] (1+x*A(x))^(2*n+1)/(2*n+1): */

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

(PARI) {a(n, m=1)=if(n==0, 1, if(m==0, 0^n, sum(k=0, n, m*binomial(2*n+m, k)/(2*n+m)*a(n-k, k))))}

CROSSREFS

Cf. A215505, A215506, A215507.

Cf. A182224, A002449, A030266, A087949, A088714, A091713, A120971.

Sequence in context: A190761 A005700 A220911 * A111538 A324237 A230218

Adjacent sequences:  A088714 A088715 A088716 * A088718 A088719 A088720

KEYWORD

nonn,eigen

AUTHOR

Paul D. Hanna, Oct 12 2003 and Mar 10 2007

STATUS

approved

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Last modified January 23 03:52 EST 2021. Contains 340384 sequences. (Running on oeis4.)