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A181567 Triangle read by rows: T(n,k) is coefficient of k-th power in expansion of ((x^(n+1)-1)/(x-1))^n. 7
1, 1, 1, 1, 2, 3, 2, 1, 1, 3, 6, 10, 12, 12, 10, 6, 3, 1, 1, 4, 10, 20, 35, 52, 68, 80, 85, 80, 68, 52, 35, 20, 10, 4, 1, 1, 5, 15, 35, 70, 126, 205, 305, 420, 540, 651, 735, 780, 780, 735, 651, 540, 420, 305, 205, 126, 70, 35, 15, 5, 1, 1, 6, 21, 56, 126, 252, 462, 786, 1251 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

In each row n>=0, k takes values from 0 to n^2 inclusive. Row sums equal A000169(n+1). All rows are palindromic. Row n is also row n of the (n+1)-nomial array (e.g., row 1 is also row 1 of A007318).

T(n,k) gives the number of divisors of A181555(n) with k prime factors counted with multiplicity. See also A001222, A071207, A146291, A146292.

T(n,k) is the number of size k submultisets of the so-called regular multiset {1_1,1_2,...,1_(n-1),1_n, ... ,i_1,i_2,...,i_(n-1),i_n, ... ,n_1,n_2,...,n_(n-1),n_n} (which contains n copies of i for 0 < i < n). - Thomas Wieder, Dec 28 2013

LINKS

Alois P. Heinz, Rows n = 0..32, flattened

Anonymous, Polynomial calculator

Thomas Wieder, A181567 as Excel table

G. Xiao, WIMS server, Factoris (both expands and factors polynomials)

EXAMPLE

Rows begin:

1;

1,1;

1,2,3,2,1;

1,3,6,10,12,12,10,6,3,1;...

T(n=3,k=4) = 12 because we have 12 submultisets (without regard of the order of elements) of size k=4 for the regular multiset (n=3) {1, 1, 1, 2, 2, 2, 3, 3, 3}: {1, 1, 1, 2}, {1, 1, 1, 3}, {1, 1, 2, 2}, {1, 1, 2, 3}, {1, 1, 3, 3}, {1, 2, 2, 2}, {1, 2, 2, 3}, {1, 2, 3, 3}, {1, 3, 3, 3}, {2, 2, 2, 3}, {2, 2, 3, 3}, {2, 3, 3, 3}.

MAPLE

b:= proc(n, k, i) option remember; `if`(k=0, 1,

     `if`(i<1, 0, add(b(n, k-j, i-1), j=0..n)))

    end:

T:= (n, k)-> b(n, k, n):

seq(seq(T(n, k), k=0..n^2), n=0..8); # Alois P. Heinz, Jul 04 2016

MATHEMATICA

row[n_] := CoefficientList[((x^(n+1) - 1)/(x-1))^n + O[x]^(n^2+1), x]; Table[row[n], {n, 0, 6}] // Flatten (* Jean-Fran├žois Alcover, Apr 06 2017 *)

CROSSREFS

A163181 gives row n of n-nomial array. See also A000012, A007318, A027907, A008287, A035343, A063260, A063265, A171890.

Sequence in context: A027907 A026323 A017838 * A058294 A323834 A082868

Adjacent sequences:  A181564 A181565 A181566 * A181568 A181569 A181570

KEYWORD

easy,nonn,tabf

AUTHOR

Matthew Vandermast, Oct 31 2010

STATUS

approved

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Last modified May 25 11:07 EDT 2020. Contains 334592 sequences. (Running on oeis4.)