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.

A008305 Triangle read by rows: a(n,k) = number of permutations of [n] allowing i->i+j (mod n), j=0..k-1.

Original entry on oeis.org

1, 1, 2, 1, 2, 6, 1, 2, 9, 24, 1, 2, 13, 44, 120, 1, 2, 20, 80, 265, 720, 1, 2, 31, 144, 579, 1854, 5040, 1, 2, 49, 264, 1265, 4738, 14833, 40320, 1, 2, 78, 484, 2783, 12072, 43387, 133496, 362880, 1, 2, 125, 888, 6208, 30818, 126565, 439792, 1334961, 3628800
Offset: 1

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Comments

The point is, we are counting permutations of [n] = {1,2,...,n} with the restriction that i cannot move by more than k places. Hence the phrase "permutations with restricted displacements". - N. J. A. Sloane, Mar 07 2014
The triangle could have been defined as an infinite square array by setting a(n,k) = n! for k >= n.

Examples

			a(4,3) = 9 because 9 permutations of {1,2,3,4} are allowed if each i can be placed on 3 positions i+0, i+1, i+2 (mod 4): 1234, 1423, 1432, 3124, 3214, 3412, 4123, 4132, 4213.
Triangle begins:
  1,
  1, 2,
  1, 2,   6,
  1, 2,   9,  24,
  1, 2,  13,  44,  120,
  1, 2,  20,  80,  265,   720,
  1, 2,  31, 144,  579,  1854,   5040,
  1, 2,  49, 264, 1265,  4738,  14833,  40320,
  1, 2,  78, 484, 2783, 12072,  43387, 133496,  362880,
  1, 2, 125, 888, 6208, 30818, 126565, 439792, 1334961, 3628800,
  ...
		

References

  • H. Minc, Permanents, Encyc. Math. #6, 1978, p. 48

Crossrefs

Diagonals (from the right): A000142, A000166, A000179, A000183, A004307, A189389, A184965.
Diagonals (from the left): A000211 or A048162, 4*A000382 or A004306 or A000803, A000804, A000805.
a(n,ceiling(n/2)) gives A306738.

Programs

  • Maple
    with(LinearAlgebra):
    a:= (n, k)-> Permanent(Matrix(n,
                 (i, j)-> `if`(0<=j-i and j-i
    				
  • Mathematica
    a[n_, k_] := Permanent[Table[If[0 <= j-i && j-i < k || j-i < k-n, 1, 0], {i, 1,n}, {j, 1, n}]]; Table[Table[a[n, k], {k, 1, n}], {n, 1, 10}] // Flatten (* Jean-François Alcover, Mar 10 2014, after Alois P. Heinz *)

Formula

a(n,k) = per(sum(P^j, j=0..k-1)), where P is n X n, P[ i, i+1 (mod n) ]=1, 0's otherwise.
a(n,n) - a(n,n-1) = A002467(n). - Alois P. Heinz, Mar 06 2019

Extensions

Comments and more terms from Len Smiley
More terms from Vladeta Jovovic, Oct 02 2003
Edited by Alois P. Heinz, Dec 18 2010

A000804 Permanent of a certain cyclic n X n (0,1) matrix.

Original entry on oeis.org

1, 1, 2, 6, 24, 120, 265, 579, 1265, 2783, 6208, 13909, 31337, 70985, 161545, 369024, 845825, 1944295, 4480285, 10345391, 23930320, 55435605, 128577253, 298529333, 693718721, 1613210120, 3753680073, 8738534315, 20351593033, 47413960239, 110493496000
Offset: 0

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Comments

a(n) is the number of permutations of [ n ] allowing i->i+j (mod n), j=0..4.

References

  • 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).

Crossrefs

Cf. A000805.
Fifth column of triangle A008305. - Vladeta Jovovic, Oct 03 2003
Cf. A260074. - Alois P. Heinz, Jul 14 2015

Programs

  • Maple
    a:= n-> `if`(n<5, n!, (Matrix(11, (i,j)-> if i+1=j then 1 elif i=11 then [-1, -1, 2, 2, 4, 2, -6, -2, -2, 0, 3][j] else 0 fi)^(n+6). <<41, -16, 33, -1, 5, -1, 16, 5, 13, 29, 65>>)[1,1]): seq(a(n), n=0..30);
  • Mathematica
    a[n_] := If[n<5, n!, ((Table[Which[i+1 == j, 1, i == 11, {-1, -1, 2, 2, 4, 2, -6, -2, -2, 0, 3}[[j]], True, 0], {i, 1, 11}, {j, 1, 11}] // MatrixPower[#, n+6]&).{41, -16, 33, -1, 5, -1, 16, 5, 13, 29, 65}) // First]; Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Mar 17 2014, after Alois P. Heinz *)

Formula

G.f.: (41*x^15 +64*x^14 -48*x^13 -113*x^12 -213*x^11 -190*x^10 +122*x^9 +158*x^8 +150*x^7 +75*x^6 -60*x^5 -10*x^4 -2*x^3 +x^2 +2*x -1) / (-x^11 -x^10 +2*x^9 +2*x^8 +4*x^7 +2*x^6 -6*x^5 -2*x^4 -2*x^3 +3*x -1).

Extensions

More terms from Vladeta Jovovic, Oct 03 2003
Edited by Alois P. Heinz, Dec 18 2010

A000803 a(n+3) = a(n+2) + a(n+1) + a(n) - 4.

Original entry on oeis.org

0, 0, 8, 4, 8, 16, 24, 44, 80, 144, 264, 484, 888, 1632, 3000, 5516, 10144, 18656, 34312, 63108, 116072, 213488, 392664, 722220, 1328368, 2443248, 4493832, 8265444, 15202520, 27961792, 51429752, 94594060, 173985600, 320009408
Offset: 0

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Comments

This sequence and A004306 coincide from the term "24" onwards. This follows easily by studying the two g.f.'s. - R. J. Mathar and Andrew S. Plewe, Dec 04 2007

References

  • 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).

Crossrefs

Programs

  • Haskell
    a000803 n = a000803_list !! n
    a000803_list = 0 : 0 : 8 : zipWith (+)
                   (tail $ zipWith (+) (tail a000803_list) a000803_list)
                   (map (subtract 4) a000803_list)
    -- Reinhard Zumkeller, Nov 18 2011
    
  • Mathematica
    LinearRecurrence[{2,0,0,-1},{0,0,8,4},40] (* Harvey P. Dale, Mar 25 2013 *)
  • PARI
    concat([0,0],Vec((8-12*x)/(1-2*x+x^4)+O(x^97))) \\ Charles R Greathouse IV, Nov 18 2011

Formula

G.f.: -4x^2*(3x-2) /((x-1)(x^3+x^2+x-1)) = 2(-5x^2+1)/(x^3+x^2+x-1)-2/(x-1). - R. J. Mathar, Dec 04 2007
a(0)=0, a(1)=0, a(2)=8, a(3)=4, a(n) = 2*a(n-1) - a(n-4). - Harvey P. Dale, Mar 25 2013

Extensions

More terms from Larry Reeves (larryr(AT)acm.org), Mar 17 2000
Showing 1-3 of 3 results.