A219538 G.f. satisfies A(x) = 1 + x*A(x)^2*(1 + A(x))^2/2.

1, 2, 12, 98, 924, 9468, 102432, 1151410, 13315692, 157406876, 1893480264, 23103024084, 285233168760, 3556744196000, 44730062281800, 566683825859730, 7225564521956940, 92653105887920556, 1194068058333608136, 15457771628663418748, 200916876963088849992

Offset

0,2

Links

G. C. Greubel, Table of n, a(n) for n = 0..870

Formula

Let F(x) = (1-x - sqrt(1 - 4*x)) / x, then g.f. A(x) satisfies:

(1) A(x) = sqrt( (1/x)*Series_Reversion(x/F(x)^2) ),

(2) A(x) = F(x*A(x)^2) and F(x) = A(x/F(x)^2),

where F(x) = 2*C(x) - 1 such that C(x) = 1 + x*C(x)^2 is the g.f. of the Catalan numbers (A000108).

Let G(x) be the g.f. of A100327, then g.f. A(x) satisfies:

(3) A(x) = (1/x)*Series_Reversion(x/G(x)),

(4) A(x) = G(x*A(x)) and G(x) = A(x/G(x)).

Recurrence: 3*n*(3*n-1)*(3*n+1)*(11*n-14)*a(n) = 3*(2*n-1)*(693*n^3 - 1575*n^2 + 1026*n - 176)*a(n-1) + 2*(n-2)*(2*n-3)*(2*n-1)*(11*n-3)*a(n-2). - Vaclav Kotesovec, Dec 28 2013

a(n) ~ sqrt(242+66*sqrt(33)) * (7+11/9*sqrt(33))^n / (66*sqrt(Pi) * n^(3/2)). - Vaclav Kotesovec, Dec 28 2013

a(n) = (1/n) * Sum_{k=0..floor(n-1)/2} 2^(n-2*k) * binomial(n,k) * binomial(3*n-k,n-1-2*k) for n > 0. - Seiichi Manyama, Apr 02 2024

Example

G.f.: A(x) = 1 + 2*x + 12*x^2 + 98*x^3 + 924*x^4 + 9468*x^5 + 102432*x^6 +...
Related expansions:
A(x)^2 = 1 + 4*x + 28*x^2 + 244*x^3 + 2384*x^4 + 24984*x^5 +...
A(2)^3 = 1 + 6*x + 48*x^2 + 446*x^3 + 4524*x^4 + 48588*x^5 +...
A(2)^4 = 1 + 8*x + 72*x^2 + 712*x^3 + 7504*x^4 + 82704*x^5 +...
where A(x) = 1 + x*(A(x)^2 + 2*A(x)^3 + A(x)^4)/2.
The g.f. satisfies A(x) = F(x*A(x)^2) and F(x) = A(x/F(x)^2) where
F(x) = 1 + 2*x + 4*x^2 + 10*x^3 + 28*x^4 + 84*x^5 + 264*x^6 +...+ 2*A000108(n)*x^n +...
The g.f. satisfies A(x) = G(x*A(x)) and G(x) = A(x/G(x)) where
G(x) = 1 + 2*x + 8*x^2 + 42*x^3 + 252*x^4 + 1636*x^5 +...+ A100327(n)*x^n +...

Mathematica

CoefficientList[Sqrt[1/x*InverseSeries[Series[x^3/(1-x-Sqrt[1-4*x])^2, {x, 0, 20}], x]], x] (* Vaclav Kotesovec, Dec 28 2013 *)

Prog

(PARI) /* Formula A(x) = 1 + x*A(x)^2*(1 + A(x))^2/2: */
{a(n)=local(A=1); for(i=1, n, A=1+x*A^2*(1+A +x*O(x^n))^2/2); polcoeff(A, n)}
for(n=0, 25, print1(a(n), ", "))
(PARI) /* Formula using Series Reversion involving Catalan numbers: */
{a(n)=local(A=1); A=(1-x-sqrt(1-4*x +x^3*O(x^n)))/x; polcoeff(sqrt(1/x*serreverse(x/A^2)), n)}
for(n=0, 25, print1(a(n), ", "))

Crossrefs

Cf. A068875, A100327.

Cf. A219534, A219537, A371658.

Sequence in context: A095338 A308820 A322717 * A245897 A231173 A303203

Adjacent sequences: A219535 A219536 A219537 * A219539 A219540 A219541

Keyword

nonn

Author

Paul D. Hanna, Nov 22 2012

Status

approved