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A127359 a(n) = Sum_{k=0..n} C(n,floor(k/2))*3^(n-k). 5
1, 4, 14, 48, 162, 544, 1820, 6080, 20290, 67680, 225684, 752448, 2508468, 8362176, 27875064, 92919168, 309734850, 1032458080, 3441543140, 11471842880, 38239537852, 127465249344, 424884399624, 1416281802368, 4720940242612, 15736469278144, 52454901060680 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Hankel transform is (-2)^n. In general, given r>=0, the sequence given by Sum_{k=0..n} C(n,floor(k/2))*r^(n-k) has Hankel transform (1-r)^n. The sequence is the image of the sequence with g.f. (1+x)/(1-3x) under the Chebyshev mapping g(x)->(1/sqrt(1-4x^2))*g(xc(x^2)), where c(x) is the g.f. of the Catalan numbers A000108.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..300

FORMULA

G.f.: (1/sqrt(1-4x^2))*(1+x*c(x^2))/(1-3*x*c(x^2)).

a(n) = Sum_{k=0..n} A061554(n,k)*3^k. [Philippe Deléham, Dec 04 2009]

Recurrence: 3*n*a(n) = 2*(5*n + 3)*a(n-1) + 4*(3*n - 11)*a(n-2) - 40*(n-2)*a(n-3). - Vaclav Kotesovec, Oct 19 2012

a(n) ~ 4*10^n/3^(n+1). - Vaclav Kotesovec, Oct 19 2012

MAPLE

A127359:=n->sum(binomial(n, floor(k/2))*3^(n-k), k=0..n): seq(A127359(n), n=0..30); # Wesley Ivan Hurt, Mar 14 2015

MATHEMATICA

Table[Sum[Binomial[n, Floor[k/2]]*3^(n-k), {k, 0, n}], {n, 0, 20}] (* Vaclav Kotesovec, Oct 19 2012 *)

CROSSREFS

Cf. A107430 [From Philippe Deléham, Sep 16 2009]

Cf. A000108 (Catalan numbers).

Sequence in context: A047135 A291254 A248957 * A289928 A007070 A204089

Adjacent sequences:  A127356 A127357 A127358 * A127360 A127361 A127362

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Jan 11 2007

STATUS

approved

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Last modified February 21 10:49 EST 2019. Contains 320372 sequences. (Running on oeis4.)