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.

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A342313 T(n, k) = (n + k - 1)*(n + k)*binomial(2*n + 1, n - k + 1) with T(0, 0) = T(1, 0) = 1. Triangle read by rows, T(n, k) for 0 <= k <= n.

Original entry on oeis.org

1, 1, 6, 20, 60, 60, 210, 420, 420, 210, 1512, 2520, 2520, 1512, 504, 9240, 13860, 13860, 9240, 3960, 990, 51480, 72072, 72072, 51480, 25740, 8580, 1716, 270270, 360360, 360360, 270270, 150150, 60060, 16380, 2730, 1361360, 1750320, 1750320, 1361360, 816816, 371280, 123760, 28560, 4080
Offset: 0

Views

Author

Peter Luschny, Mar 08 2021

Keywords

Comments

The triangle can be seen as representing the denominators of a sequence of rational polynomials. Let p_{n}(x) = Sum_{k=0..n} (A342312(n, k)/T(n, k))*x^k. Then p_{n}(1) = B_{n}(1), where B_{n}(x) are the Bernoulli polynomials. See A342312 for a formula for the polynomials.

Examples

			Triangle starts:
[0] 1
[1] 1,       6
[2] 20,      60,      60
[3] 210,     420,     420,     210
[4] 1512,    2520,    2520,    1512,    504
[5] 9240,    13860,   13860,   9240,    3960,   990
[6] 51480,   72072,   72072,   51480,   25740,  8580,   1716
[7] 270270,  360360,  360360,  270270,  150150, 60060,  16380,  2730
[8] 1361360, 1750320, 1750320, 1361360, 816816, 371280, 123760, 28560, 4080
		

Crossrefs

Cf. A069072 (main diagonal), A342312 (numerators).

Programs

  • Maple
    T := (n, k) -> `if`(n=0, 1,`if`(n=1 and k=0, 1,
    (n + k - 1)*(n + k)*binomial(2*n + 1, n - k + 1))):
    seq(print(seq(T(n, k), k = 0..n)), n = 0..8);
  • Mathematica
    T[0, 0] := 1; T[1, 0] := 1;
    T[n_, k_] := (n - 1 + k) (n + k) Binomial[2n + 1, n - k + 1];
    Table[T[n, k], {n, 0, 8}, {k, 0, n}]

A342321 T(n, k) = A343277(n)*[x^k] p(n, x) where p(n, x) = (1/(n+1))*Sum_{k=0..n} (-1)^k*E1(n, k)*x^(n - k) / binomial(n, k), and E1(n, k) are the Eulerian numbers A123125. Triangle read by rows, for 0 <= k <= n.

Original entry on oeis.org

1, 0, 1, 0, -1, 2, 0, 1, -4, 3, 0, -3, 22, -33, 12, 0, 1, -13, 33, -26, 5, 0, -5, 114, -453, 604, -285, 30, 0, 5, -200, 1191, -2416, 1985, -600, 35, 0, -35, 2470, -21465, 62476, -78095, 42930, -8645, 280, 0, 14, -1757, 21912, -88234, 156190, -132351, 51128, -7028, 126
Offset: 0

Views

Author

Peter Luschny, Mar 09 2021

Keywords

Comments

Conjecture: For even n >= 6 p(n, x)/x and for odd n >= 3 p(n, x)/(x^2 - x) is irreducible.

Examples

			Triangle starts:
[n]                T(n, k)                      A343277(n)
----------------------------------------------------------
[0] 1;                                                 [1]
[1] 0,  1;                                             [2]
[2] 0, -1,     2;                                      [6]
[3] 0,  1,    -4,     3;                              [12]
[4] 0, -3,    22,   -33,    12;                       [60]
[5] 0,  1,   -13,    33,   -26,     5;                [30]
[6] 0, -5,   114,  -453,   604,  -285,    30;        [210]
[7] 0,  5,  -200,  1191, -2416,  1985,  -600,  35;   [280]
.
The coefficients of the polynomials p(n, x) = (Sum_{k = 0..n} T(n, k) x^k) / A343277(n) for the first few n:
[0] 1;
[1] 0,   1/2;
[2] 0,  -1/6,    1/3;
[3] 0,  1/12,   -1/3,    1/4;
[4] 0, -1/20,   11/30, -11/20,    1/5;
[5] 0,  1/30,  -13/30,  11/10,  -13/15,  1/6.
		

Crossrefs

Sequences of rational polynomials p(n, x) with p(n, 1) = Bernoulli(n, 1):

Programs

  • Maple
    CoeffList := p -> op(PolynomialTools:-CoefficientList(p,x)):
    E1 := (n, k) -> combinat:-eulerian1(n, k):
    poly := n -> (1/(n+1))*add((-1)^k*E1(n,k)*x^(n-k)/binomial(n,k), k=0..n):
    Trow := n -> denom(poly(n))*CoeffList(poly(n)): seq(Trow(n), n = 0..9);
  • Mathematica
    Poly342321[n_, x_] := If[n == 0, 1, Sum[x^k*k!*Sum[(-1)^(n - j)*StirlingS2[n, j] /((k - j)!(n - j + 1) Binomial[n + 1, j]), {j, 0, k}], {k, 1, n}]];
    Table[A343277[n] CoefficientList[Poly342321[n, x], x][[k+1]], {n, 0, 9}, {k, 0, n}] // Flatten

Formula

An alternative representation of the sequence of rational polynomials is:
p(n, x) = Sum_{k=1..n} x^k*k!*Sum_{j=0..k} (-1)^(n-j)*Stirling2(n, j)/((k - j)!(n - j + 1)*binomial(n + 1, j)) for n >= 1 and p(0, x) = 1.
(Sum_{k = 0..n} T(n, k)) / A343277(n) = Bernoulli(n, 1).
Showing 1-2 of 2 results.