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A200376 G.f.: 1/sqrt(1-10*x^2 + x^4/(1-8*x^2)) + x/(1-9*x^2). 2
1, 1, 5, 9, 37, 81, 301, 729, 2549, 6561, 22045, 59049, 193029, 531441, 1703469, 4782969, 15111573, 43046721, 134539837, 387420489, 1200901157, 3486784401, 10739313997, 31381059609, 96172251061, 282429536481, 862142190941, 2541865828329, 7734936371269, 22876792454961, 69439155241581 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..30.

FORMULA

G.f. satisfies: A(x) = sqrt(1 + 2*x*A(x) + 9*x^2*A(x)^2). - Paul D. Hanna, Nov 18 2014

Let G(x) = g.f. of A200375, then g.f. A(x) satisfies:

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

(2) A(x) = G(x/A(x)) and G(x) = A(x*G(x)),

where A200375(n) = A000108(n)*A001045(n), the product of Catalan and Jacobsthal numbers.

a(n) ~ 3^(n-1). - Vaclav Kotesovec, Jun 29 2013

EXAMPLE

G.f.: A(x) = 1 + x + 5*x^2 + 9*x^3 + 37*x^4 + 81*x^5 + 301*x^6 + 729*x^7 +...

The g.f. of A200375(n) = A000108(n)*A001045(n) begins:

G(x) = 1 + x + 2*3*x^2 + 5*5*x^3 + 14*11*x^4 + 42*21*x^5 + 132*43*x^6 +...

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

Conjecture: n*a(n) +(n-1)*a(n-1) +(24-17*n)*a(n-2) +(41-17*n)*a(n-3) +72*(n-3)*a(n-4) +72*(n-4)*a(n-5)=0. - R. J. Mathar, Nov 17 2011

MATHEMATICA

CoefficientList[Series[1/Sqrt[1-10x^2+x^4/(1-8x^2)]+x/(1-9x^2), {x, 0, 30}], x] (* Harvey P. Dale, Nov 19 2011 *)

PROG

(PARI) {a(n)=polcoeff(1/sqrt(1-10*x^2 + x^4/(1-8*x^2 +x*O(x^n))) + x/(1-9*x^2 +x*O(x^n)), n)}

for(n=0, 30, print1(a(n), ", "))

(PARI) {a(n)=local(G=sum(m=0, n, binomial(2*m, m)/(m+1)*polcoeff(1/(1-x-2*x^2+x*O(x^m)), m)*x^m)+x*O(x^n)); polcoeff(x/serreverse(x*G), n)}

for(n=0, 30, print1(a(n), ", "))

CROSSREFS

Cf. A200375, A098615, A098617.

Sequence in context: A239546 A083832 A070969 * A098477 A243762 A303801

Adjacent sequences:  A200373 A200374 A200375 * A200377 A200378 A200379

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Nov 16 2011

STATUS

approved

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Last modified December 14 09:18 EST 2019. Contains 329979 sequences. (Running on oeis4.)