The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A271961 G.f. A(x) satisfies: A( 4*A(x)^2 - 16*A(x)^3 ) = 4*x^2. 6

%I

%S 1,2,6,48,350,2624,19788,164352,1375222,11676672,100528724,879042560,

%T 7766216812,69183897600,621144540056,5617045733376,51099366332838,

%U 467284485996544,4293452339931012,39617950774198272,366977680831584068,3411064524143329280,31806303401026218792,297435647894402105344,2788846295384191083196,26212988486868078166016,246938491597204310266696

%N G.f. A(x) satisfies: A( 4*A(x)^2 - 16*A(x)^3 ) = 4*x^2.

%H Paul D. Hanna, <a href="/A271961/b271961.txt">Table of n, a(n) for n = 1..300</a>

%F Let B(x) be the series reversion of g.f. A(x), so that A(B(x)) = x, then

%F (1) 4*B(x)^2 = A( 4*x^2 - 16*x^3 ),

%F (2) B(4*x^2) = 4*A(x)^2 - 16*A(x)^3,

%F (3) B(4*B(x)^2) = 4*x^2 - 16*x^3.

%F a(n) ~ c * d^n / n^(3/2), where d = 9.97390550579080951... and c = 0.0367046946616235... - _Vaclav Kotesovec_, Aug 28 2017

%e G.f.: A(x) = x + 2*x^2 + 6*x^3 + 48*x^4 + 350*x^5 + 2624*x^6 + 19788*x^7 + 164352*x^8 + 1375222*x^9 + 11676672*x^10 + 100528724*x^11 +...

%e where A( 4*A(x)^2 - 16*A(x)^3 ) = 4*x^2.

%e RELATED SERIES.

%e A(x)^2 = x^2 + 4*x^3 + 16*x^4 + 120*x^5 + 928*x^6 + 7224*x^7 + 56576*x^8 + 472944*x^9 + 4019712*x^10 + 34562904*x^11 + 300781568*x^12 +...

%e A(x)^3 = x^3 + 6*x^4 + 30*x^5 + 224*x^6 + 1806*x^7 + 14592*x^8 + 118236*x^9 + 1001472*x^10 + 8640726*x^11 + 75300864*x^12 +...

%e Note that 4*A(x)^2 - 16*A(x)^3 is an even function:

%e 4*A(x)^2 - 16*A(x)^3 = 4*x^2 - 32*x^4 + 128*x^6 - 7168*x^8 + 55296*x^10 - 1687552*x^12 + 41222144*x^14 - 1329070080*x^16 +...

%e Let B(x) be the series reversion of g.f. A(x) such that A(B(x)) = x, then

%e B(x) = x - 2*x^2 + 2*x^3 - 28*x^4 + 54*x^5 - 412*x^6 + 2516*x^7 - 20280*x^8 + 133670*x^9 - 888620*x^10 + 6071548*x^11 - 41120904*x^12 +...

%e such that 4*B(x)^2 = A(4*x^2 - 16*x^3) and B(4*x^2) = 4*A(x)^2 - 16*A(x)^3.

%o (PARI) {a(n) = my(A=[1],F=x); for(i=1,n, A=concat(A,0); F=x*Ser(A); A[#A] = -Vec(subst(F,x,4*F^2 - 16*F^3))[#A]/8); A[n]}

%o for(n=1,30, print1(a(n),", "))

%o (PARI) {a(n) = my(A=x); for(i=0,n, A = serreverse(sqrt(subst(A/4,x,4*x^2 - 16*x^3 + x^2*O(x^n))))); polcoeff(A,n)}

%o for(n=1,30,print1(a(n),", ")) \\ _Paul D. Hanna_, Aug 11 2017

%Y f. A291313.

%K nonn

%O 1,2

%A _Paul D. Hanna_, Apr 21 2016

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 1 07:45 EDT 2021. Contains 346384 sequences. (Running on oeis4.)