A006134 a(n) = Sum_{k=0..n} binomial(2*k,k). (Formerly M2811)

1, 3, 9, 29, 99, 351, 1275, 4707, 17577, 66197, 250953, 956385, 3660541, 14061141, 54177741, 209295261, 810375651, 3143981871, 12219117171, 47564380971, 185410909791, 723668784231, 2827767747951, 11061198475551, 43308802158651

Offset

0,2

Comments

The expression a(n) = B^n*Sum_{ k=0..n } binomial(2*k,k)/B^k gives A006134 for B=1, A082590 (B=2), A132310 (B=3), A002457 (B=4), A144635 (B=5). - N. J. A. Sloane, Jan 21 2009

T(n+1,1) from table A045912 of characteristic polynomial of negative Pascal matrix. - Michael Somos, Jul 24 2002

p divides a((p-3)/2) for p=11, 13, 23, 37, 47, 59, 61, 71, 73, 83, 97, 107, 109, 131, 157, 167, ...: A097933. Also primes congruent to {1, 2, 3, 11} mod 12 or primes p such that 3 is a square mod p (excluding 2 and 3) A038874. - Alexander Adamchuk, Jul 05 2006

Partial sums of the even central binomial coefficients. For p prime >=5, a(p-1) = 1 or -1 (mod p) according as p = 1 or -1 (mod 3) (see Pan and Sun link). - David Callan, Nov 29 2007

First column of triangle A187887. - Michel Marcus, Jun 23 2013

From Gus Wiseman, Apr 20 2023: (Start)

Also the number of nonempty subsets of {1,...,2n+1} with median n+1, where the median of a multiset is either the middle part (for odd length), or the average of the two middle parts (for even length). The odd/even-length cases are A000984 and A006134(n-1). For example, the a(0) = 1 through a(2) = 9 subsets are:

{1} {2} {3}

{1,3} {1,5}

{1,2,3} {2,4}

{1,3,4}

{1,3,5}

{2,3,4}

{2,3,5}

{1,2,4,5}

{1,2,3,4,5}

Alternatively, a(n-1) is the number of nonempty subsets of {1,...,2n-1} with median n.

(End)

References

Marko Petkovsek, Herbert Wilf and Doron Zeilberger, A=B, A K Peters, 1996, p. 22.

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

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Moa Apagodu and Doron Zeilberger, Using the "Freshman's Dream" to Prove Combinatorial Congruences, arXiv:1606.03351 [math.CO], 2016. Also Amer. Math. Monthly. 124 (2017), 597-608.

Paul Barry, Jacobsthal Decompositions of Pascal's Triangle, Ternary Trees, and Alternating Sign Matrices, Journal of Integer Sequences, 19 (2016), Article 16.3.5.

Hacène Belbachir, Abdelghani Mehdaoui and László Szalay, Diagonal Sums in the Pascal Pyramid, II: Applications, J. Int. Seq., Vol. 22 (2019), Article 19.3.5.

J. Hietarinta, T. Mase and R. Willox, Algebraic entropy computations for lattice equations: why initial value problems do matter, arXiv:1909.03232 [nlin.SI], 2019.

Neelam J. Kumar, N-Summet-k and Its Application in the Construction of Pascal Triangle and Pascal Matrix, Journal of Applied Mathematics and Physics, 4 (2016), 169-177.

W. F. Lunnon, The Pascal matrix, Fib. Quart., Vol. 15 (1977), pp. 201-204.

Kim McInturff and Rob Pratt, Representations of a generating function, The College Mathematics Journal, 40 (2009), 294-296.

Hao Pan and Zhi-Wei Sun, A combinatorial identity with application to Catalan numbers, arXiv:math/0509648 [math.CO], 2005-2006.

Peter Paule, A proof of a conjecture of Knuth. Experiment. Math. 5, No. 2 (1996), 83-89. MR1418955 (97k:33004).

Mehtaab Sawhney, proposer, Problem 1102 Problems and Solutions, The College Mathematics Journal, Vol. 48, No. 3 (May 2017), pp. 219-225, p. 219; Radouan Boukharfane, A binomial identity, Solution to Problem 1102, ibid., Vol. 49, No. 3 (May 2018), pp. 225-226.

Wikipedia, Pascal Matrix.

Formula

From Alexander Adamchuk, Jul 05 2006: (Start)

a(n) = Sum_{k=0..n} (2k)!/(k!)^2.

a(n) = A066796(n) + 1, n>0. (End)

G.f.: 1/((1-x)*sqrt(1-4*x)).

D-finite with recurrence: (n+2)*a(n+2) - (5*n+8)*a(n+1) + 2*(2*n+3)*a(n) = 0. - Emanuele Munarini, Mar 15 2011

a(n) = C(2n,n) * Sum_{k=0..2n} (-1)^k*trinomial(n,k)/C(2n,k) where trinomial(n,k) = [x^k] (1 + x + x^2)^n. E.g. a(2) = C(4,2)*(1/1 - 2/4 + 3/6 - 2/4 + 1/1) = 6*(3/2) = 9 ; a(3) = C(6,3)*(1/1 - 3/6 + 6/15 - 7/20 + 6/15 - 3/6 + 1/1) = 20*(29/20) = 29. - Paul D. Hanna, Aug 21 2007

From Alzhekeyev Ascar M, Jan 19 2012: (Start)

a(n) = Sum_{ k=0..n } b(k)*binomial(n+k,k), where b(k)=0 for n-k == 2 (mod 3), b(k)=1 for n-k == 0 or 1 (mod 6), and b(k)=-1 for n-k== 3 or 4 (mod 6).

a(n) = Sum_{ k=0..n-1 } c(k)*binomial(2n,k) + binomial(2n,n), where c(k)=0 for n-k == 0 (mod 3), c(k)=1 for n-k== 1 (mod 3), and c(k)=-1 for n-k==2 (mod 3). (End)

a(n) ~ 2^(2*n+2)/(3*sqrt(Pi*n)). - Vaclav Kotesovec, Nov 06 2012

G.f.: G(0)/2/(1-x), where G(k)= 1 + 1/(1 - 2*x*(2*k+1)/(2*x*(2*k+1) + (k+1)/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, May 24 2013

G.f.: G(0)/(1-x), where G(k)= 1 + 4*x*(4*k+1)/( (4*k+2) - x*(4*k+2)*(4*k+3)/(x*(4*k+3) + (k+1)/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, Jun 26 2013

a(n) = Sum_{k = 0..n} binomial(n+1,k+1)*A002426(k). - Peter Bala, Oct 29 2015

a(n) = -binomial(2*(n+1),n+1)*hypergeom([1,n+3/2],[n+2], 4) - i/sqrt(3). - Peter Luschny, Oct 29 2015

a(n) = binomial(2*n, n)*hypergeom([1,-n], [1/2-n], 1/4). - Peter Luschny, Mar 16 2016

From Gus Wiseman, Apr 20 2023: (Start)

a(n+1) - a(n) = A000984(n).

a(n) = A013580(2n+1,n+1) (conjectured).

a(n) = 2*A024718(n) - 1.

a(n) = A100066(2n+1).

a(n) = A231147(2n+1,n+1) (conjectured). (End)

a(n) = Sum_{k=0..floor(n/3)} 3^(n-3*k) * binomial(n-k,2*k) * binomial(2*k,k) (Sawhney, 2017). - Amiram Eldar, Feb 24 2024

From Mélika Tebni, Feb 27 2024: (Start)

Limit_{n -> oo} a(n) / A281593(n) = 2.

E.g.f.: exp(2*x)*BesselI(0,2*x) + exp(x)*integral( BesselI(0,2*x)*exp(x) ) dx. (End)

Example

1 + 3*x + 9*x^2 + 29*x^3 + 99*x^4 + 351*x^5 + 1275*x^6 + 4707*x^7 + 17577*x^8 + ...

Maple

A006134 := proc(n) sum(binomial(2*k, k), k=0..n); end;
a := n -> -binomial(2*(n+1), n+1)*hypergeom([1, n+3/2], [n+2], 4) - I/sqrt(3):
seq(simplify(a(n)), n=0..24); # Peter Luschny, Oct 29 2015
# third program:
A006134 := series(exp(2*x)*BesselI(0, 2*x) + exp(x)*int(BesselI(0, 2*x)*exp(x), x), x = 0, 25):
seq(n!*coeff(A006134, x, n), n=0..24); # Mélika Tebni, Feb 27 2024

Mathematica

Table[Sum[((2k)!/(k!)^2), {k, 0, n}], {n, 0, 50}] (* Alexander Adamchuk, Jul 05 2006 *)
a[ n_] := (4/3) Binomial[ 2 n, n] Hypergeometric2F1[ 1/2, 1, -n + 1/2, -1/3] (* Michael Somos, Jun 20 2012 *)
Accumulate[Table[Binomial[2n, n], {n, 0, 30}]] (* Harvey P. Dale, Jan 11 2015 *)
CoefficientList[Series[1/((1 - x) Sqrt[1 - 4 x]), {x, 0, 33}], x] (* Vincenzo Librandi, Aug 13 2015 *)

Prog

(MATLAB) n=10; x=pascal(n); trace(x)
(PARI) {a(n) = if( n<0, 0, polcoeff( charpoly( matrix( n+1, n+1, i, j, -binomial( i+j-2, i-1))), 1))} \\ Michael Somos, Jul 10 2002
(PARI) {a(n)=binomial(2*n, n)*sum(k=0, 2*n, (-1)^k*polcoeff((1+x+x^2)^n, k)/binomial(2*n, k))} \\ Paul D. Hanna, Aug 21 2007
(PARI) my(x='x+O('x^100)); Vec(1/((1-x)*sqrt(1-4*x))) \\ Altug Alkan, Oct 29 2015
(Maxima) makelist(sum(binomial(2*k, k), k, 0, n), n, 0, 12); \\ Emanuele Munarini, Mar 15 2011
(Magma) &cat[ [&+[ Binomial(2*k, k): k in [0..n]]]: n in [0..30]]; // Vincenzo Librandi, Aug 13 2015

Crossrefs

Cf. A000984 (first differences), A097933, A038874, A132310.

Cf. A006135, A006136, A045912.

Equals A066796 + 1.

Odd bisection of A100066.

Row sums of A361654 (also column k = 2).

A007318 counts subsets by length, A231147 by median, A013580 by integer median.

A359893 and A359901 count partitions by median.

Cf. A000975, A024718, A057552, A079309, A327481.

Sequence in context: A151030 A066331 A099780 * A074526 A231291 A239116

Adjacent sequences: A006131 A006132 A006133 * A006135 A006136 A006137

Keyword

nonn

Author

N. J. A. Sloane

Extensions

Simpler definition from Alexander Adamchuk, Jul 05 2006

Status

approved