login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A260650 G.f. satisfies: A(x)^2 = A( x^2/(1-4*x)^2 ). 3
1, 4, 18, 88, 455, 2444, 13486, 75912, 433935, 2511388, 14684422, 86611848, 514704064, 3078845696, 18523994024, 112026315616, 680626958899, 4152411174284, 25428402204982, 156247439709832, 963048223399984, 5952595420121536, 36887847899094888, 229132114803540320, 1426367728966653535, 8897049258366111004 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Radius of convergence is r = (9 - sqrt(17))/32 where r = r^2/(1-4*r)^2 with A(r) = 1.

Compare to: C(x)^2 = C( x^2/(1-2*x)^2 ) where C(x) = (1-2*x-sqrt(1-4*x))/(2*x) is a g.f. of the Catalan numbers, A000108.

LINKS

Table of n, a(n) for n=1..26.

FORMULA

G.f. satisfies:

(1) A(x) = -A( -x/(1-8*x) ).

(2) A(x^2) = A( x/(1+4*x) )^2 = A( -x/(1-4*x) )^2.

(3) A( x/(1+2*x)^2 ) = -A( -x/(1-2*x)^2 ), an odd function.

(4) A( x/(1+2*x)^2 )^2 = A( x^2/(1+4*x^2)^2 ), an even function.

EXAMPLE

G.f.: A(x) = x + 4*x^2 + 18*x^3 + 88*x^4 + 455*x^5 + 2444*x^6 + 13486*x^7 + 75912*x^8 + 433935*x^9 + 2511388*x^10 + 14684422*x^11 + 86611848*x^12 +...

where A( x^2/(1-4*x)^2 ) = A(x)^2,

A( x^2/(1-4*x)^2 ) = x^2 + 8*x^3 + 52*x^4 + 320*x^5 + 1938*x^6 + 11696*x^7 + 70648*x^8 + 427776*x^9 + 2597831*x^10 + 15824664*x^11 + 96687516*x^12 +...

Also, A( x/(1+4*x) ) = A(x^2)^(1/2),

A( x/(1+4*x) ) = x + 2*x^3 + 7*x^5 + 30*x^7 + 143*x^9 + 726*x^11 + 3840*x^13 + 20904*x^15 + 116275*x^17 + 657798*x^19 + 3772912*x^21 + 21890152*x^23 +...

Let B(x) = x/Series_Reversion( A(x) ), so that A(x) = x*B(A(x)), then

B(x) = 1 + 4*x + 2*x^2 - x^4 + 2*x^6 - 5*x^8 + 12*x^10 - 30*x^12 + 82*x^14 - 233*x^16 + 668*x^18 - 1949*x^20 + 5802*x^22 +...+ A107087(n)*x^(2*n) +...

such that B(x) = F(x^2) + 4*x = F(x)^2 where F(x) is the g.f. of A107087.

PROG

(PARI) {a(n) = my(A=x); for(i=1, #binary(n+1), A = sqrt( subst(A, x, x^2/(1-4*x +x*O(x^n))^2) ) ); polcoeff(A, n)}

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

CROSSREFS

Cf. A264232, A264224, A107087, A107088.

Sequence in context: A083879 A081671 A244785 * A006629 A068764 A127394

Adjacent sequences:  A260647 A260648 A260649 * A260651 A260652 A260653

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Nov 16 2015

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy .

Last modified February 20 18:41 EST 2018. Contains 299381 sequences. (Running on oeis4.)