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A103882 a(n) = Sum_{i=0..n} C(n+1,i)*C(n-1,i-1)*C(2n-i,n). 4
1, 2, 12, 92, 780, 7002, 65226, 623576, 6077196, 60110030, 601585512, 6078578508, 61908797418, 634756203018, 6545498596110, 67830161708592, 705951252118284, 7375213677918294, 77310179609631564, 812839595630249540, 8569327862277434280, 90562666977432643862 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Number of permutations of n copies of 1..3 with all adjacent differences <= 1 in absolute value. - R. H. Hardin, May 06 2010 [Cf. A177316. - Peter Bala, Jan 14 2020]

LINKS

R. H. Hardin and Alois P. Heinz, Table of n, a(n) for n = 0..950 (terms n=1..94 from R. H. Hardin)

A. Straub, Multivariate Apéry numbers and supercongruences of rational functions, arXiv:1401.0854 [math.NT] (2014).

FORMULA

a(n) = (A005258(n-1)+3*A005258(n))/5 (Apéry numbers). - Mark van Hoeij, Jul 13 2010

n^2*(n-1)*(5*n-8)*a(n) = (n-1)*(55*n^3-143*n^2+102*n-24)*a(n-1) + n*(n-2)^2*(5*n-3)*a(n-2). - Alois P. Heinz, Jun 29 2015

a(n) ~ phi^(5*n + 3/2) / (2*Pi*5^(1/4)*n), where phi = A001622 = (1+sqrt(5))/2 is the golden ratio. - Vaclav Kotesovec, Jul 21 2019

From Peter Bala, Jan 14 2020: (Start)

a(n) = Sum_{k = 0..n} C(n, k)^2*C(n+k-1, k). Cf. A005258.

Supercongruences: for any prime p >= 5, a(n*p^k) == a(n*p^(k-1)) ( mod p^(3*k) ) for all positive integers n and k (follows from known supercongruences satisfied by the Apéry numbers A005258 - see Straub, Example 3.4). (End)

a(n) = hypergeom([-n, -n, n], [1, 1], 1). - Peter Luschny, Jan 19 2020

MAPLE

a:= proc(n) option remember; `if`(n<2, n+1,

      ((n-1)*(55*n^3-143*n^2+102*n-24)*a(n-1)+

      n*(5*n-3)*(n-2)^2*a(n-2))/((n-1)*(5*n-8)*n^2))

    end:

seq(a(n), n=0..30);  # Alois P. Heinz, Jun 29 2015

# Alternative:

a := n -> hypergeom([-n, -n, n], [1, 1], 1):

seq(simplify(a(n)), n=0..21); # Peter Luschny, Jan 19 2020

MATHEMATICA

Drop[Table[Sum[Sum[Multinomial[r, g, n + 1 - r - g] Binomial[n - 1, n - r] Binomial[n - 1, n - g], {g, 1, n}], {r, 1, n}], {n, 0, 18}], 1] (* Geoffrey Critzer, Jun 29 2015 *)

PROG

(MAGMA) [1] cat [&+[Binomial(n+1, i)*Binomial(n-1, i-1) * Binomial(2*n-i, n): i in [0..n]]:n in  [1..21]]; // Marius A. Burtea, Jan 19 2020

(MAGMA) [&+[Binomial(n, k)^2*Binomial(n+k-1, k): k in [0..n]]:n in  [0..21]]; // Marius A. Burtea, Jan 19 2020

CROSSREFS

Equals A103881(n, n). Cf. A005258, A177316.

Row n=3 of A331562.

Sequence in context: A225573 A155639 A333473 * A304979 A003123 A316143

Adjacent sequences:  A103879 A103880 A103881 * A103883 A103884 A103885

KEYWORD

nonn,easy

AUTHOR

Ralf Stephan, Feb 20 2005

EXTENSIONS

a(0)=1 prepended by Alois P. Heinz, Jun 29 2015

STATUS

approved

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Last modified July 13 08:26 EDT 2020. Contains 335685 sequences. (Running on oeis4.)