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A002893 Sum_{k=0..n} binomial(n,k)^2 * binomial(2k,k).
(Formerly M2998 N1214)
22
1, 3, 15, 93, 639, 4653, 35169, 272835, 2157759, 17319837, 140668065, 1153462995, 9533639025, 79326566595, 663835030335, 5582724468093, 47152425626559, 399769750195965, 3400775573443089, 29016970072920387, 248256043372999089 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

This is the Taylor expansion of a special point on a curve described by Beauville. - Matthijs Coster, Apr 28 2004

a(n) is the (2n)th moment of the distance from the origin of a 3-step random walk in the plane. - Peter M. W. Gill (peter.gill(AT)nott.ac.uk), Feb 27 2004

a(n) is the number of Abelian squares of length 2n over a 3-letter alphabet. [From Jeffrey Shallit, Aug 17 2010]

Consider 2D simple random walk on honeycomb lattice. a(n) gives number of paths of length 2n ending at origin. - Sergey Perepechko Feb 16 2011

Row sums of the square of A008459. - Peter Bala, Mar 05 2013

Conjecture: For each n=1,2,3,... the polynomial g_n(x) = sum_{k=0}^n binomial(n,k)^2*binomial(2k,k)*x^k is irreducible over the field of rational numbers. [Zhi-Wei Sun, Mar 21 2013]

REFERENCES

P. Barrucand, A combinatorial identity, Problem 75-4, SIAM Rev., 17 (1975), 168.

Arnaud Beauville, Les familles stables de courbes sur P_1 admettant quatre fibres singulieres, Comptes Rendus, Academie Science Paris, no. 294, May 24 1982.

Jonathan M. Borwein and Armin Straub, Mahler measures, short walks and log-sine integrals, http://carma.newcastle.edu.au/~jb616/wmi-paper.pdf.

J. M. Borwein, A. Straub and J. Wan, Three-Step and Four-Step Random Walk Integrals, Exper. Math., 22 (2013), 1-14.

Matthijs Coster, Over 6 families van krommen [On 6 families of curves], Master's Thesis (unpublished), Aug 26 1983.

C. Domb, On the theory of cooperative phenomena in crystals, Advances in Phys., 9 (1960), 149-361.

J. A. Hendrickson, Jr., On the enumeration of rectangular (0,1)-matrices, Journal of Statistical Computation and Simulation, 51 (1995), 291-313.

M. Klamkin, ed., Problems in Applied Mathematics: Selections from SIAM Review, SIAM, 1990; see pp. 148-149.

L. B. Richmond and J. Shallit, Counting abelian squares, Electronic J. Combinatorics 16 (1), #R72, June 2009.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Armin Straub, Arithmetic aspects of random walks and methods in definite integration, Ph. D. Dissertation, School Of Science And Engineering, Tulane University, 2012. - From N. J. A. Sloane, Dec 16 2012

LINKS

T. D. Noe, Table of n, a(n) for n=0..100

David H. Bailey, Jonathan M. Borwein, David Broadhurst and M. L. Glasser, Elliptic integral evaluations of Bessel moments, arXiv:0801.0891.

Jonathan M. Borwein, Dirk Nuyens, Armin Straub and James Wan, Random Walk Integrals, 2010.

E. Delaygue, Arithmetic properties of Apery-like numbers, arXiv preprint arXiv:1310.4131, 2013

V. J. W. Guo, Proof of two conjectures of Z.-W. Sun on congruences for Franel numbers, Arxiv preprint arXiv:1201.0617, 2012

L. B. Richmond and J. Shallit, Counting abelian squares, Electronic J. Combinatorics 16 (1), #R72, June 2009. [From Jeffrey Shallit, Aug 17 2010]

Z.-W. Sun, Congruences for Franel numbers, Arxiv preprint arXiv:1112.1034, 2011.

Yi Wang and Bao-Xuan Zhu, Proofs of some conjectures on monotonicity of number-theoretic and combinatorial sequences, arXiv preprint arXiv:1303.5595, 2013

FORMULA

a(n) = Sum_{m=0..n} binomial(n, m) * A000172(m). [Barrucand]

(n+1)^2 a(n+1) = (10*n^2+10*n+3) * a(n) - 9*n^2 * a(n-1). - Matthijs Coster, Apr 28 2004

Sum_{n>=0} a(n)x^n/n!^2 = BesselI(0, 2*sqrt(x))^3. - Vladeta Jovovic, Mar 11 2003

a(n) = Sum_{p+q+r=n} (n!/(p!q!r!))^2 with p,q,r >=0. - Michael Somos, Jul 25 2007

a(n) = 3*A087457(n) for n>0. [From Philippe Deléham, Sep 14 2008]

a(n) = hypergeom([1/2, -n, -n], [1, 1], 4). [From Mark van Hoeij, Jun 02 2010]

G.f.: 2*sqrt(2)/Pi/sqrt(1-6*z-3*z^2+sqrt((1-z)^3*(1-9*z))) *  EllipticK(8*z^(3/2)/(1-6*z-3*z^2+sqrt((1-z)^3*(1-9*z)))). - Sergey Perepechko, Feb 16 2011

G.f.: Sum_{n>=0} (3*n)!/n!^3 * x^(2*n)*(1-x)^n / (1-3*x)^(3*n+1). [Paul D. Hanna, Feb 26 2012]

Asymptotic: a(n) ~ 3^(2*n+3/2)/(4*Pi*n). [Vaclav Kotesovec, Sep 11 2012]

G.f.: 1/(1-3*x)*(1-6*x^2*(1-x)/(Q(0)+6*x^2*(1-x))), where Q(k)= (54*x^3 - 54*x^2 + 9*x -1)*k^2 + (81*x^3 - 81*x^2 + 18*x -2)*k + 33*x^3 - 33*x^2 +9*x - 1 - 3*x^2*(1-x)*(1-3*x)^3*(k+1)^2*(3*k+4)*(3*k+5)/Q(k+1) ; (continued fraction). - Sergei N. Gladkovskii, Jul 16 2013

G.f.: G(0)/(2*(1-9*x)^(2/3) ), where G(k)= 1 + 1/(1 - 3*(3*k+1)^2*x*(1-x)^2/(3*(3*k+1)^2*x*(1-x)^2 - (k+1)^2*(1-9*x)^2/G(k+1) )); (continued fraction). - Sergei N. Gladkovskii, Jul 31 2013

EXAMPLE

G.f.: A(x) = 1 + 3*x + 15*x^2 + 93*x^3 + 639*x^4 + 4653*x^5 + 35169*x^6 +...

G.f.: A(x) = 1/(1-3*x) + 6*x^2*(1-x)/(1-3*x)^4 + 90*x^4*(1-x)^2/(1-3*x)^7 + 1680*x^6*(1-x)^3/(1-3*x)^10 + 34650*x^8*(1-x)^4/(1-3*x)^13 +... [Paul D. Hanna, Feb 26 2012]

MATHEMATICA

Table[Sum[Binomial[n, k]^2 Binomial[2k, k], {k, 0, n}], {n, 0, 20}] (* Harvey P. Dale, Aug 19 2011 *)

a[ n_] := If[n < 0, 0, HypergeometricPFQ[{1/2, -n, -n}, {1, 1}, 4]] (* Michael Somos, Oct 16 2013 *)

a[n_] := SeriesCoefficient[BesselI[0, 2*Sqrt[x]]^3, {x, 0, n}]*n!^2; Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Dec 30 2013 *)

PROG

(PARI) {a(n) = if( n<0, 0, n!^2 * polcoeff( besseli(0, 2*x + O(x^(2*n+1)))^3, 2*n))}

(PARI) {a(n)= sum(k=0, n, binomial(n, k)^2 * binomial(2*k, k))} /* Michael Somos, Jul 25 2007 */

(PARI) {a(n)=polcoeff(sum(m=0, n, (3*m)!/m!^3 * x^(2*m)*(1-x)^m / (1-3*x+x*O(x^n))^(3*m+1)), n)} \\ Paul D. Hanna, Feb 26 2012

CROSSREFS

Cf. A000172, A002895, A000984.

Cf. A169714 and A169715.-  Peter Bala, Mar 05 2013

Sequence in context: A231657 A193661 A192296 * A074539 A103210 A203014

Adjacent sequences:  A002890 A002891 A002892 * A002894 A002895 A002896

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Mar 29 2003

STATUS

approved

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Last modified September 19 15:54 EDT 2014. Contains 246977 sequences.