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A215506 G.f. satisfies: A(x) = 1 + x*A(x)^4*A(x*A(x)^4). 3
1, 1, 5, 39, 387, 4516, 59522, 864981, 13641761, 230931591, 4162594198, 79412758356, 1595971048438, 33662065586127, 742852904575909, 17107642358401929, 410242691108675077, 10223836926997402818, 264339609703677876178, 7079673476173815446742 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..19.

FORMULA

a(n) = coefficient of x^n in (1+x*A(x))^(4*n+1)/(4*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*binomial(4*n+m,k)/(4*n+m) * a(n-k,k).

G.f. A(x) = F(x,1) where F(x,n) satisfies: F(x,n) = F(x,n-1)*(1 + x*F(x,n)^3*F(x,n+1)) for n>0 with F(x,0)=1.

EXAMPLE

G.f.: A(x) = 1 + x + 5*x^2 + 39*x^3 + 387*x^4 + 4516*x^5 + 59522*x^6 +...

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

A = 1 + x*A^3*B;

B = A*(1 + x*B^3*C);

C = B*(1 + x*C^3*D);

D = C*(1 + x*D^3*E);

E = D*(1 + x*E^3*F); ...

where B(x) = A(x)*A(x*A(x)^4), C(x) = A(x)*B(x*A(x)^4),  D(x) = A(x)*C(x*A(x)^4), ...

Expansions of a few of the functions described above begin:

B(x) = 1 + 2*x + 15*x^2 + 158*x^3 + 1991*x^4 + 28283*x^5 + 439880*x^6 +...

C(x) = 1 + 3*x + 30*x^2 + 402*x^3 + 6257*x^4 + 107405*x^5 + 1983027*x^6 +...

D(x) = 1 + 4*x + 50*x^2 + 816*x^3 + 15215*x^4 + 308986*x^5 + 6679230*x^6 +...

E(x) = 1 + 5*x + 75*x^2 + 1445*x^3 + 31480*x^4 + 741075*x^5 + 18447355*x^6 +...

ALTERNATE GENERATING METHOD.

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

A = 1 + x*A^4*B,

B = 1 + x*(A*B)^4*C,

C = 1 + x*(A*B*C)^4*D,

D = 1 + x*(A*B*C*D)^4*E, etc.,

then B(x) = A(x*A(x)^4), C(x) = B(x*A(x)^4), D(x) = C(x*A(x)^4), etc.,

where A(x) = 1 + x*A(x)^4*A(x*A(x)^4) is the g.f. of this sequence.

Expansions of a few of the functions described above begin:

B(x) = 1 + x + 9*x^2 + 105*x^3 + 1415*x^4 + 21089*x^5 + 340100*x^6 +...

C(x) = 1 + x + 13*x^2 + 203*x^3 + 3507*x^4 + 65018*x^5 + 1274266*x^6 +...

D(x) = 1 + x + 17*x^2 + 333*x^3 + 7047*x^4 + 157359*x^5 + 3665076*x^6 +...

E(x) = 1 + x + 21*x^2 + 495*x^3 + 12419*x^4 + 325312*x^5 + 8813506*x^6 +...

PROG

(PARI) {a(n)=local(A=1+x); for(i=0, n, A=1+x*A^4*subst(A, x, x*A^4+x*O(x^n))); polcoeff(A, n)}

(PARI) /* a(n) = [x^n] (1+x*A(x))^(4*n+1)/(4*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))^(4*m+1)/(4*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(4*n+m, k)/(4*n+m)*a(n-k, k))))}

for(n=0, 41, print1(a(n), ", "))

CROSSREFS

Cf. A088717, A215505, A215507.

Sequence in context: A129763 A277424 A182954 * A316654 A070767 A124549

Adjacent sequences:  A215503 A215504 A215505 * A215507 A215508 A215509

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Aug 13 2012

STATUS

approved

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Last modified October 22 13:06 EDT 2018. Contains 316459 sequences. (Running on oeis4.)