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A059298

Triangle of idempotent numbers binomial(n,k)*k^(n-k), version 2.

1, 2, 1, 3, 6, 1, 4, 24, 12, 1, 5, 80, 90, 20, 1, 6, 240, 540, 240, 30, 1, 7, 672, 2835, 2240, 525, 42, 1, 8, 1792, 13608, 17920, 7000, 1008, 56, 1, 9, 4608, 61236, 129024, 78750, 18144, 1764, 72, 1, 10, 11520, 262440, 860160, 787500, 272160, 41160

(list; table; graph; refs; listen; history; text; internal format)

OFFSET

0,2

COMMENTS

The inverse triangle is the signed version 1,-2,1,9,-6,1,.. of triangle A061356. - Peter Luschny, Mar 13 2009

T(n,k) is the sum of the products of the cardinality of the blocks (cells) in the set partitions of {1,2,..,n} into exactly k blocks.

From Peter Bala, Jul 22 2014: (Start)

Exponential Riordan array [(1+x)*exp(x), x*exp(x)].

Let M = A093375, the exponential Riordan array [(1+x)*exp(x), x], and for k = 0,1,2,... define M(k) to be the lower unit triangular block array

/I_k 0\

\ 0 M/

having the k x k identity matrix I_k as the upper left block; in particular, M(0) = M. The present triangle equals the infinite matrix product M(0)*M(1)*M(2)*... - see the Example section. (End)

The Bell transform of n+1. For the definition of the Bell transform see A264428. - Peter Luschny, Jan 18 2016

REFERENCES

L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 91, #43 and p. 135, [3i'].

LINKS

G. C. Greubel, Table of n, a(n) for the first 50 rows, flattened

Eric Weisstein's World of Mathematics, Idempotent Number

EXAMPLE

Triangle begins

2, 1;

3, 6, 1;

4, 24, 12, 1; ...

From Peter Bala, Jul 22 2014: (Start)

With the arrays M(k) as defined in the Comments section, the infinite product M(0)*M(1)*M(2)*... begins

/1 \/1 \/1 \ /1 \

|2 1 ||0 1 ||0 1 | |2 1 |

|3 4 1 ||0 2 1 ||0 0 1 |... = |3 6 1 |

|4 9 6 1 ||0 3 4 1 ||0 0 2 1 | |4 24 12 1 |

|5 16 18 8 1||0 4 9 6 1||0 0 3 4 1| |5 80 90 20 1|

|... ||... ||... | |... | (End)

MAPLE

T:= (n, k)-> binomial(n+1, k+1)*(k+1)^(n-k): seq(seq(T(n, k), k=0..n), n=0..10); # Georg Fischer, Oct 27 2021

MATHEMATICA

t = Transpose[ Table[ Range[0, 11]! CoefficientList[ Series[(x Exp[x])^n/n!, {x, 0, 11}], x], {n, 11}]]; Table[ t[[n, k]], {n, 2, 11}, {k, n - 1}] // Flatten (* or simply *)

t[n_, k_] := Binomial[n, k]*k^(n - k); Table[t[n, k], {n, 10}, {k, n}] // Flatten

PROG

(Magma) /* As triangle */ [[Binomial(n, k)*k^(n-k): k in [1..n]]: n in [1.. 15]]; // Vincenzo Librandi, Aug 22 2015

(SageMath) # uses[bell_matrix from A264428]

# Adds a column 1, 0, 0, 0, ... at the left side of the triangle.

bell_matrix(lambda n: n+1, 10) # Peter Luschny, Jan 18 2016

(PARI) for(n=1, 25, for(k=1, n, print1(binomial(n, k)*k^(n-k), ", "))) \\ G. C. Greubel, Jan 05 2017

CROSSREFS

There are 4 versions: A059297, A059298, A059299, A059300.

Diagonals give A001788, A036216, A040075, A050982, A002378, 3*A002417, etc.

Row sums are A000248. A093375.

Sequence in context: A120257 A337412 A337408 * A214306 A337411 A337407