

A128014


Central binomial coefficients C(2n,n) repeated.


13



1, 1, 2, 2, 6, 6, 20, 20, 70, 70, 252, 252, 924, 924, 3432, 3432, 12870, 12870, 48620, 48620, 184756, 184756, 705432, 705432, 2704156, 2704156, 10400600, 10400600, 40116600, 40116600, 155117520, 155117520, 601080390, 601080390
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

0,3


COMMENTS

Binomial transform is A097893. Hankel transform is A128017.
Hankel transform of a(n+1) is A128018.  Paul Barry, Nov 23 2009
Number of 2nbead balanced binary necklaces that are equivalent to their reverse.  Andrew Howroyd, Sep 29 2017
Number of ballot sequences of length n in which the vote is tied or decided by 1 vote.  Nachum Dershowitz, Aug 12 2020
Number of binary strings of length n that are abelian squares.  Michael S. Branicky, Dec 21 2020


LINKS

Table of n, a(n) for n=0..33.


FORMULA

G.f.: (1+x)/sqrt(14*x^2).
a(n) = C(n,n/2)*(1+(1)^n)/2 + C(n1,(n1)/2)*(1(1)^n)/2.
a(n) = (1/Pi)*Integral_{x=2..2} x^n*(1+x)/(x*sqrt(4x^2)), as moment sequence.
E.g.f. of a(n+1): Bessel_I(0,2*x)+2*Bessel_I(1,2*x).  Paul Barry, Mar 26 2010
n*a(n) +(n2)*a(n1) +4*(n+1)*a(n2) +4*(n+3)*a(n3) = 0.  R. J. Mathar, Nov 26 2012
a(n) = 2^n*Product_{k=0..n1} ((k/n+1/n)/2)^((1)^k).  Peter Luschny, Dec 03 2013
Fom Reinhard Zumkeller, Nov 14 2014: (Start)
a(n) = A000984(floor(n/2)).
a(n) = A249095(n,n) = A249308(n) / 2^n. (End)


MATHEMATICA

(1+x)/Sqrt[14x^2] + O[x]^34 // CoefficientList[#, x]& (* JeanFrançois Alcover, Oct 07 2017 *)
With[{cb=Table[Binomial[2n, n], {n, 0, 20}]}, Riffle[cb, cb]] (* Harvey P. Dale, Feb 17 2020 *)


PROG

(Haskell)
a128014 = a000984 . flip div 2
 Reinhard Zumkeller, Nov 14 2014


CROSSREFS

Cf. A097893, A128017, A128018.
Cf. A000984, A249095, A249308.
Sequence in context: A309094 A109859 A128057 * A135401 A129881 A132369
Adjacent sequences: A128011 A128012 A128013 * A128015 A128016 A128017


KEYWORD

easy,nonn


AUTHOR

Paul Barry, Feb 11 2007


STATUS

approved



