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 1-4 of 4 results.

A117662 a(n) = n*(n-1)*(n-2)*(n+3)/12.

Original entry on oeis.org

0, 0, 0, 3, 14, 40, 90, 175, 308, 504, 780, 1155, 1650, 2288, 3094, 4095, 5320, 6800, 8568, 10659, 13110, 15960, 19250, 23023, 27324, 32200, 37700, 43875, 50778, 58464, 66990, 76415, 86800, 98208, 110704, 124355, 139230, 155400, 172938, 191919
Offset: 0

Views

Author

Roger L. Bagula, Apr 11 2006

Keywords

Comments

Also, the number of external intersections of the diagonals of a general n-gon = (A176145) - (A000332). - Michel Lagneau, Apr 21 2010

Crossrefs

Essentially the same as A050297 and A005701.

Programs

  • Magma
    [n*(n-1)*(n-2)*(n+3)/12: n in [0..50]]; // Vincenzo Librandi, Oct 10 2013
  • Maple
    seq(n*(n-1)*(n-2)*(n+3)/12, n=0..40); # Wesley Ivan Hurt, Oct 10 2013
  • Mathematica
    Table[n(n-1)(n-2)(n+3)/12, {n,0,100}] (* Wesley Ivan Hurt, Sep 26 2013 *)
    CoefficientList[Series[x^3 (3 - x)/(1 - x)^5, {x, 0, 80}], x] (* Vincenzo Librandi, Oct 10 2013 *)
    LinearRecurrence[{5,-10,10,-5,1},{0,0,0,3,14},80] (* Harvey P. Dale, Jan 01 2025 *)

Formula

G.f.: x^3*(3-x)/(1-x)^5. - Colin Barker, Jan 31 2012
From Amiram Eldar, May 17 2025: (Start)
Sum_{n>=3} 1/a(n) = 137/300.
Sum_{n>=3} (-1)^(n+1)/a(n) = 32*log(2)/5 - 1247/300. (End)

Extensions

Edited by N. J. A. Sloane, Apr 23 2006

A179898 Triangle V(l,p) (l>=0, p=0..l) read by rows: see Formula for definition, see Comments for motivation.

Original entry on oeis.org

1, 0, 1, 1, 0, 1, 0, 3, 0, 1, 3, 0, 6, 0, 1, 0, 14, 0, 10, 0, 1, 14, 0, 40, 0, 15, 0, 1, 0, 84, 0, 90, 0, 21, 0, 1, 84, 0, 300, 0, 175, 0, 28, 0, 1, 0, 594, 0, 825, 0, 308, 0, 36, 0, 1, 594, 0, 2475, 0, 1925, 0, 504, 0, 45, 0, 1, 0, 4719, 0, 7865, 0, 4004, 0, 780, 0, 55, 0, 1, 4719, 0, 22022, 0, 21021, 0, 7644, 0, 1155, 0, 66, 0, 1, 0, 40898, 0, 78078, 0, 49686, 0, 13650, 0, 1650, 0, 78, 0, 1, 40898, 0, 208208, 0, 231868, 0, 107016, 0, 23100, 0, 2288, 0, 91, 0, 1, 0, 379236, 0, 804440, 0, 606424, 0, 214200, 0, 37400, 0, 3094, 0, 105, 0, 1
Offset: 0

Views

Author

N. J. A. Sloane, Jan 30 2011

Keywords

Comments

If the triangle in A053121 is regarded as counting minimal subdiagonal paths in the first quadrant, this triangle enumerates pairs of non-crossing paths of the same type.

Examples

			Triangle begins:
  1;
  0, 1;
  1, 0, 1;
  0, 3, 0, 1;
  3, 0, 6, 0, 1;
  0, 14, 0, 10, 0, 1;
  14, 0, 40, 0, 15, 0, 1;
  0, 84, 0, 90, 0, 21, 0, 1;
  84, 0, 300, 0, 175, 0, 28, 0, 1;
  0, 594, 0, 825, 0, 308, 0, 36, 0, 1;
  594, 0, 2475, 0, 1925, 0, 504, 0, 45, 0, 1;
  0, 4719, 0, 7865, 0, 4004, 0, 780, 0, 55, 0, 1;
  4719, 0, 22022, 0, 21021, 0, 7644, 0, 1155, 0, 66, 0, 1;
  0, 40898, 0, 78078, 0, 49686, 0, 13650, 0, 1650, 0, 78, 0, 1;
  40898, 0, 208208, 0, 231868, 0, 107016, 0, 23100, 0, 2288, 0, 91, 0, 1;
  ...
		

References

  • D. Gouyou-Beauchamps, Chemins sous-diagonaux et tableau de Young, pp. 112-125 of "Combinatoire Enumerative (Montreal 1985)", Lect. Notes Math. 1234, 1986 (see |V_{l,p}| on page 114).

Crossrefs

The first two columns are both A005700, the next column is A181571. The diagonals on the right give A000217, A005701. Row sums are A005817.

Programs

  • Maple
    V:=proc(l,p)
    if ((l-p) mod 2) = 1 then 0 else l!*(l+2)!*(p+3)! / (((l-p)/2)!*((l-p)/2+1)!*p!*((l+p)/2+2)!*((l+p)/2+3)!); fi;
    end;
    r:=n->[seq( V(n,p),p=0..n)];
    for n from 0 to 15 do lprint(r(n)); od:
  • Mathematica
    v[l_, p_] := If[Mod[l-p, 2] == 1, 0, l!*(l+2)!*(p+3)!/(((l-p)/2)!*((l-p)/2+1)!*p!*((l+p)/2+2)!*((l+p)/2+3)!)]; Table[v[l, p], {l, 0, 15}, {p, 0, l}] // Flatten (* Jean-François Alcover, Jan 09 2014, translated from Maple *)

Formula

V(l,p) = 0 if l and p have opposite parity, otherwise V(l,p) = l!*(l+2)!*(p+3)!/(((l-p)/2)!*((l-p)/2+1)!*p!*((l+p)/2+2)!*((l+p)/2+3)!).

A050297 Number of scalars which can be constructed from the Riemann tensor and metric tensor in n dimensions.

Original entry on oeis.org

0, 1, 3, 14, 40, 90, 175, 308, 504, 780, 1155, 1650, 2288, 3094, 4095, 5320, 6800, 8568, 10659, 13110, 15960, 19250, 23023, 27324, 32200, 37700, 43875, 50778, 58464, 66990, 76415, 86800, 98208, 110704, 124355, 139230, 155400, 172938
Offset: 1

Views

Author

Keywords

Crossrefs

Cf. A005701.

Programs

  • Magma
    [0,1] cat [n*(n-1)*(n-2)*(n+3)/12: n in [3..60]]; // Vincenzo Librandi, May 13 2017
  • Mathematica
    CoefficientList[Series[x^2*(x^5 - 5*x^4 + 10*x^3 - 9*x^2 + 2*x - 1)/(x - 1)^5, {x, 0, 50}], x] (* G. C. Greubel, May 12 2017 *)
    Join[{0, 1}, Table[n (n - 1) (n - 2) (n + 3) / 12, {n, 3, 40}]] (* Vincenzo Librandi, May 13 2017 *)
  • PARI
    my(x='x+O('x^50)); concat([0], Vec(x^2*(x^5-5*x^4+10*x^3-9*x^2+2*x-1)/(x-1)^5)) \\ G. C. Greubel, May 12 2017
    

Formula

a(2) = 1, otherwise a(n) = n*(n-1)*(n-2)*(n+3)/12 = A005701(n-3).
From Chai Wah Wu, Aug 31 2016: (Start)
a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n > 7.
G.f.: x^2*(x^5 - 5*x^4 + 10*x^3 - 9*x^2 + 2*x - 1)/(x - 1)^5. (End)
From Amiram Eldar, May 22 2025: (Start)
Sum_{n>=2} 1/a(n) = 437/300.
Sum_{n>=2} (-1)^n/a(n) = 1547/300 - 32*log(2)/5. (End)

A181571 Third column of triangle in A179898.

Original entry on oeis.org

1, 6, 40, 300, 2475, 22022, 208208, 2068560, 21414900, 229523800, 2533942752, 28698821320, 332357673375, 3925129083750, 47167131780000, 575637606165600, 7123515376299300, 89266155250239000, 1131410294476020000, 14489559984061890000, 187330691180608155180, 2443121585638964379864
Offset: 1

Views

Author

N. J. A. Sloane, Jan 30 2011

Keywords

Crossrefs

Showing 1-4 of 4 results.