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.

A122766 Triangle read by rows: let p(n, x) = x*p(n-1, x) - p(n-2, x), then T(n, x) = d^2/dx^2 (p(n, x)).

Original entry on oeis.org

2, -2, 6, -6, -6, 12, 6, -24, -12, 20, 12, 24, -60, -20, 30, -12, 60, 60, -120, -30, 42, -20, -60, 180, 120, -210, -42, 56, 20, -120, -180, 420, 210, -336, -56, 72, 30, 120, -420, -420, 840, 336, -504, -72, 90, -30, 210, 420, -1120, -840, 1512, 504, -720, -90, 110
Offset: 1

Views

Author

Roger L. Bagula and Gary W. Adamson, Sep 22 2006

Keywords

Examples

			Triangle begins as:
    2;
   -2,    6;
   -6,    6,   12;
    6,  -24,  -12,   20;
   12,   24,  -60,  -20,   30;
   12,   60,   60, -120,  -30,   42;
  -20,  -60,  180,  120, -210,  -42,  56;
   20, -120, -180,  420,  210, -336, -56,  72;

Links

Crossrefs

Cf. A000217, A046854, A066170, A122765, A130777.

Programs

  • Magma
    A122766:= func< n,k | 2*(-1)^Binomial(n-k+1, 2)*Binomial(k+1,2)*Binomial(Floor((n+k+2)/2), k+1) >;
[A122766(n,k): k in [1..n], n in [1..14]]; // G. C. Greubel, Dec 31 2022
  • Mathematica
    (* First program *)
p[0, x]=1; p[1, x]=x-1; p[k_, x_]:= p[k, x]= x*p[k-1, x] -p[k-2, x]; b = Table[Expand[p[n,x]], {n,0,15}]; Table[CoefficientList[D[b[[n]], {x,2}], x], {n,2,14}]//Flatten
(* Second program *)
T[n_, k_]:= 2*(-1)^Binomial[n-k+1,2]*Binomial[k+1,2]*Binomial[Floor[(n +k+2)/2], k+1]; Table[T[n,k], {n,14}, {k,n}]//Flatten (* G. C. Greubel, Dec 31 2022 *)
  • PARI
    tpol(n) = if (n <= 0, 1, if (n == 1, x -1, x*tpol(n-1) - tpol(n-2)));
lista(nn) = {for(n=0, nn, pol = deriv(deriv(tpol(n))); for (k=0, poldegree(pol), print1(polcoeff(pol, k), ", ");););} \\ Michel Marcus, Feb 07 2014
  • SageMath
    def A122766(n, k): return 2*(-1)^binomial(n-k+1,2)*binomial(k+1,2)*binomial(((n+k+2)//2), k+1)
flatten([[A122766(n, k) for k in range(1, n+1)] for n in range(1, 15)]) # G. C. Greubel, Dec 31 2022

Formula

From G. C. Greubel, Dec 31 2022: (Start)
T(n, k) = 2*(-1)^binomial(n-k+1, 2)*binomial(k+1,2)*binomial(floor((n+k +2)/2), k+1).
T(n, 1) = 2*(-1)^binomial(n,2)*binomial(floor((n+3)/2), 2)
T(n, n) = 2*A000217(n).
Sum_{k=1..n} T(n, k) = 2*A104555(n).
Sum_{k=1..floor((n+1)/2)} T(n-k+1, k) = 2*([n=1] - [n=2]). (End)

Extensions

Edited by N. J. A. Sloane, Oct 01 2006
Name corrected and more terms from Michel Marcus, Feb 07 2014

A209235 Rectangular array read by antidiagonals, with entry k in row n given by T(n,k) = 2^{k-1}*Sum_{j=1..n} (cos((2*j-1)*Pi/(2*n+1)))^{k-1}.

Original entry on oeis.org

1, 2, 1, 3, 1, 1, 4, 1, 3, 1, 5, 1, 5, 4, 1, 6, 1, 7, 4, 7, 1, 8, 1, 11, 4, 19, 16, 18, 1, 9, 1, 13, 4, 25, 16, 38, 29, 1, 10, 1, 15, 4, 31, 16, 58, 57, 47, 1, 11, 1, 17, 4, 37, 16, 78, 64, 117, 76, 1, 12, 1, 19, 4, 43, 16, 98, 64, 187, 193, 123, 1
Offset: 1

Views

Author

L. Edson Jeffery, Jan 12 2013

Keywords

Comments

Antidiagonal sums: {1,3,5,9,16,26,46,78,136,...}.

Examples

			Array begins as
.1..1...1..1...1...1
.2..1...3..4...7..11
.3..1...5..4..13..16
.4..1...7..4..19..16
.5..1...9..4..25..16
.6..1..11..4..31..16

Crossrefs

Rows: cf. A000012, A000032, A094649, A189234, A216605, etc.
Cf. A185095, A186740.

Formula

T(n,k) = 2^{k-1}*Sum_{j=1..n} (cos((2*j-1)*Pi/(2*n+1)))^{k-1}.
Empirical g.f. for row n: F(x) = (Sum_{u=0..n-1} A122765(n,n-1-u)*x^u)/(Sum_{v=0..n} A108299(n,v)*x^v).
Empirical: odd column first differences tend to A000984 = {1, 2, 6, 20, 70, 252, ...} (central binomial coefficients).

A123951 A polynomial of matrices is used to make a triangular sequence. The upper triangular antidiagonal Steinbach matrices are summed over their characteristic polynomial triangular sequences to give a new sequence of matrices: the characteristic polynomials of these new summed matrices are, then, used to make up this triangular sequence.

Original entry on oeis.org

1, 1, -1, -1, -1, 1, -1, -3, 4, -1, 37, -88, 69, -19, 1, 10879, -14344, 6831, -1375, 99, -1, -4322473, -40529664, -17486038, 3188841, -40896, -2346, 1, -11384127259974047, -783824545942228, 1058675233347, 505084925760, -64007100, -32568519, 23164, -1, -121986767767877481129923
Offset: 1

Views

Author

Roger L. Bagula and Gary W. Adamson, Oct 26 2006

Keywords

Comments

Basically everything is done twice. The determinants get very large very fast for these matrices: Table[Det[w[[d]]], {d, 1, Length[w]}] {1, -1, -1, 37, 10879, -4322473, -11384127259974047, -121986767767877481129923, -323621163456130064854374309178100414058036559, 189651898964129252384795657180434913387386019400002936829101989683}

Examples

			{1},
{1, -1},
{-1, -1, 1},
{-1, -3, 4, -1},
{37, -88, 69, -19,1},
{10879, -14344, 6831, -1375, 99, -1},
{-4322473, -40529664, -17486038, 3188841, -40896, -2346, 1}

Links

Crossrefs

Cf. A122765, A122771.

Programs

  • Mathematica
    An[d_] := Table[If[n + m - 1 > d, 0, 1], {n, 1, d}, {m, 1, d}]; a = Join[{{1}}, Table[CoefficientList[CharacteristicPolynomial[An[d],x], x], {d, 1, 20}]]; w = Join[{{{1}}}, Table[Sum[MatrixPower[a[[n]][[m + 1]]*An[n], m - 1], {m, 0, Length[a[[n]]] - 1}], {n, 2, 10}]]; Join[{{1}}, Table[CoefficientList[CharacteristicPolynomial[w[[d]], x], x], {d, 1, Length[w]}]]; Flatten[%]

Formula

p(n,x) = CharacteristicPolynomial(a(i,j)) p(n,x)->t(n,m) b(i,j) = Sum[t(i,j).a(j,k).{j,1,m}] p'(n,x) = CharacteristicPolynomial(b(i,j)) p'(n,x)->t'(n,m).
Showing 1-3 of 3 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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