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A047969 Square array of nexus numbers a(n,k) = (n+1)^(k+1) - n^(k+1) (n >= 0, k >= 0) read by antidiagonals. 23
1, 1, 1, 1, 3, 1, 1, 5, 7, 1, 1, 7, 19, 15, 1, 1, 9, 37, 65, 31, 1, 1, 11, 61, 175, 211, 63, 1, 1, 13, 91, 369, 781, 665, 127, 1, 1, 15, 127, 671, 2101, 3367, 2059, 255, 1, 1, 17, 169, 1105, 4651, 11529, 14197, 6305, 511, 1, 1, 19, 217, 1695, 9031 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

If each row started with an initial 0 (i.e., a(n,k) = (n+1)^k - n^k) then each row would be the binomial transform of the preceding row. - Henry Bottomley, May 31 2001

a(n-1, k-1) is the number of ordered k-tuples of positive integers such that the largest of these integers is n. - Alford Arnold, Sep 07 2005

From Alford Arnold, Jul 21 2006: (Start)

The sequences in A047969 can also be calculated using the Eulerian Array (A008292) and Pascal's Triangle (A007318) as illustrated below: (cf. A101095).

  1       1       1       1       1       1

  1       1       1       1       1       1

  -----------------------------------------

  1       2       3       4       5       6

          1       2       3       4       5

  1       3       5       7       9      11

  -----------------------------------------

  1       3       6      10      15      21

          4      12      24      40      60

                  1       3       6      10

  1       7      19      37      61      91

  -----------------------------------------

  1       4      10      20      35      56

         11      44     110     220     385

                 11      44     110     220

                          1       4      10

  1      15      65     175     369     671

  -----------------------------------------  (End)

From Peter Bala, Oct 26 2008: (Start)

The above remarks of Alford Arnold may be summarized by saying that (the transpose of) this array is the Hilbert transform of the triangle of Eulerian numbers A008292 (see A145905 for the definition of the Hilbert transform). In this context, A008292 is best viewed as the array of h-vectors of permutohedra of type A. See A108553 for the Hilbert transform of the array of h-vectors of type D permutohedra. Compare this array with A009998.

The polynomials n^k - (n-1)^k, k = 1,2,3,..., which give the nonzero entries in the columns of this array, satisfy a Riemann hypothesis: their zeros lie on the vertical line Re s = 1/2 in the complex plane. See A019538 for the connection between the polynomials n^k - (n-1)^k and the Stirling polynomials of the simplicial complexes dual to the type A permutohedra.

(End)

Empirical: (n+1)^(k+1) - n^(k+1) is the number of first differences of length k+1 arrays of numbers in 0..n, k > 0. - R. H. Hardin, Jun 30 2013

a(n-1, k-1) is the number of bargraphs of width k and height n. Examples: a(1,2) = 7 because we have [1,1,2], [1,2,1], [2,1,1], [1,2,2], [2,1,2], [2,2,1], and [2,2,2]; a(2,1) = 5 because we have [1,3], [2,3], [3,1], [3,2], and [3,3] (bargraphs are given as compositions). This comment is equivalent to A. Arnold's Sep 2005 comment. - Emeric Deutsch, Jan 30 2017

REFERENCES

J. H. Conway and R. K. Guy, The Book of Numbers, Copernicus Press, NY, 1996, p. 54.

LINKS

T. D. Noe, Rows n = 0..100 of triangle, flattened

A. Blecher, C. Brennan, A. Knopfmacher and H. Prodinger, The height and width of bargraphs, Discrete Applied Math. 180, (2015), 36-44.

Eric Weisstein's World of Mathematics, Nexus Number

FORMULA

E.g.f.: ((x-1)*e^y)/(x*e^y-1). - Vladimir Kruchinin, Jan 28 2018

T(n,m) = Sum_{k=0..m} k!*(-1)^(m+k)*Stirling2(m,k)*C(n+k-1,n), T(n,0)=1. - Vladimir Kruchinin, Jan 28 2018

EXAMPLE

Array begins:

[n\k][0  1   2    3    4   5  6  ...

[0]   1  1   1    1    1   1  1  ...

[1]   1  3   7   15   31  63  ...

[2]   1  5  19   65  211  ...

[3]   1  7  37  175  ...

MATHEMATICA

Flatten[Table[n = d - e; k = e; (n + 1)^(k + 1) - n^(k + 1), {d, 0, 100}, {e, 0, d}]] (* T. D. Noe, Feb 22 2012 *)

PROG

(Maxima)

T(n, m):=if m=0 then 1 else sum(k!*(-1)^(m+k)*stirling2(m, k)*binomial(n+k-1, n), k, 0, m); /* Vladimir Kruchinin, Jan 28 2018 */

CROSSREFS

Cf. A047970. Rows include A005917, A022521, A022522, etc.

Cf. A009998, A108553 (Hilbert transform of array of h-vectors of type D permutohedra), A145904, A145905.

Sequence in context: A119258 A099608 A247285 * A047812 A129392 A118538

Adjacent sequences:  A047966 A047967 A047968 * A047970 A047971 A047972

KEYWORD

nonn,tabl,nice,easy

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified February 23 22:17 EST 2018. Contains 299595 sequences. (Running on oeis4.)