cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-3 of 3 results.

A099022 a(n) = Sum_{k=0..n} C(n,k)*(2*n-k)!.

Original entry on oeis.org

1, 3, 38, 1158, 65304, 5900520, 780827760, 142358474160, 34209760152960, 10478436416945280, 3984884716852972800, 1842169367191937414400, 1017403495472574045158400, 661599650478455071589606400, 500354503197888042597961267200, 435447353708763072625260119808000
Offset: 0

Views

Author

Ralf Stephan, Sep 23 2004

Keywords

Comments

Diagonal of Euler-Seidel matrix with start sequence n!.
Number of ways to use the elements of {1,..,k}, n<=k<=2n, once each to form a sequence of n lists, each having length 1 or 2. - Bob Proctor, Apr 18 2005, Jun 26 2006
Replace "lists" by "sets": A105749.

Crossrefs

Cf. A001517, A076571, A082765 (binomial transform), A105749, row sums of A328826.

Programs

  • Maple
    f:= gfun:-rectoproc({a(n)=2*n*(2*n-1)*a(n-1)+n*(n-1)*a(n-2), a(0)=1,a(1)=3},a(n),remember):
    map(f, [$0..20]); # Robert Israel, Feb 15 2017
  • Mathematica
    Table[(2k)! Hypergeometric1F1[-k, -2k, 1], {k, 0, 10}] (* Vladimir Reshetnikov, Feb 16 2011 *)
    Table[Sum[Binomial[n,k](2n-k)!,{k,0,n}],{n,0,20}] (* Harvey P. Dale, Nov 22 2021 *)
  • PARI
    for(n=0,25, print1(sum(k=0,n, binomial(n,k)*(2*n-k)!), ", ")) \\ G. C. Greubel, Dec 31 2017

Formula

T(2*n, n), where T is the triangle in A076571.
a(n) = n!*A001517(n).
A082765(n) = Sum[C(n, k)*a(k), 0<=k<=n].
a(n) = 2*n*(2*n-1)*a(n-1)+n*(n-1)*a(n-2). - Vladeta Jovovic, Sep 27 2004
a(n) = int {x = 0..inf} exp(-x)*(x + x^2)^n dx. Applying the results of Nicolaescu, Section 3.2 to this integral we obtain the asymptotic expansion a(n) ~ (2*n)!*exp(1/2)*( 1 - 1/(16*n) - 191/(6144*n^2) + O(1/n^3) ). - Peter Bala, Jul 07 2014

A328921 Triangle read by rows: T(n,k) = number of vertex labeled connected Goldstone diagrams with n interactions and k external potentials.

Original entry on oeis.org

1, 2, 1, 20, 8, 1, 592, 240, 36, 2, 33888, 14208, 2400, 192, 6, 3134208, 1355520, 248640, 24000, 1200, 24, 423974400, 188052480, 36599040, 3978240, 252000, 8640, 120, 78722795520, 35613849600, 7240020480, 853977600, 62657280, 2822400, 70560, 720, 19193652817920, 8816953098240, 1851920179200
Offset: 0

Views

Author

R. J. Mathar, Oct 31 2019

Keywords

Examples

			          1;
          2           1;
         20           8           1;
        592         240          36           2;
      33888       14208        2400         192           6;
    3134208     1355520      248640       24000        1200          24;
		

Crossrefs

Formula

T(n,k) + A328922(n,k) = A328826(n,k).

A328922 Triangle T(n,k): vertex labeled disconnected Goldstone diagrams with n interactions and k external potentials.

Original entry on oeis.org

0, 0, 0, 4, 4, 1, 128, 120, 36, 4, 6432, 5952, 1920, 288, 18, 494592, 458880, 154560, 26400, 2400, 96, 55027200, 51448320, 17832960, 3279360, 352800, 21600, 600, 8455495680, 7975296000, 2819013120, 543110400, 64350720, 4798080, 211680, 4320, 1729137070080, 1644441845760, 589071974400
Offset: 0

Views

Author

R. J. Mathar, Oct 31 2019

Keywords

Examples

			         0;
         0          0;
         4          4          1;
       128        120         36          4;
      6432       5952       1920        288         18;
    494592     458880     154560      26400       2400         96;
  55027200   51448320   17832960    3279360     352800      21600        600;
8455495680 ...
		

Crossrefs

Formula

T(n,k) + A328921(n,k) = A328826(n,k).
Showing 1-3 of 3 results.