A053440 - OEIS

%I #27 Nov 19 2017 01:58:00

%S 1,3,2,7,12,6,15,50,60,24,31,180,390,360,120,63,602,2100,3360,2520,

%T 720,127,1932,10206,25200,31920,20160,5040,255,6050,46620,166824,

%U 317520,332640,181440,40320,511,18660,204630,1020600,2739240,4233600,3780000

%N Number of k-simplices in the first derived complex of the standard triangulation of an n-simplex. Equivalently, T(n,k) is the number of ascending chains of length k+1 of nonempty subsets of the set {1, 2, ..., n+1}.

%C T(n,k) is the number of length k+1 sequences of nonempty mutually disjoint subsets of {1,2,...,n+1}.  The e.g.f. for the column corresponding to k is exp(x)*(exp(x)-1)^(k+1). - _Geoffrey Critzer_, Dec 20 2011

%H G. C. Greubel, <a href="/A053440/b053440.txt">Table of n, a(n) for the first 50 rows, flattened</a>

%H F. Brenti and V. Welker, <a href="http://dx.doi.org/10.1007/s00209-007-0251-z">f-vectors of barycentric subdivisions</a> Math. Z., 259(4), 849-865, 2008.

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Barycentric_subdivision">Barycentric subdivision</a>

%F T(0,k) = delta(0,k), T(n,k) = delta(0,k) + (k+1)(T(n-1,k-1) + (k+2)T(n-1,k)).

%F E.g.f.: exp(x)*(exp(x)-1)/(1-y*(exp(x)-1)). - _Vladeta Jovovic_, Apr 13 2003

%F T(n,k) = Sum_{i = 0..n} binomial(n+1,i+1)*(k+1)!*Stirling2(i+1,k+1) = (k+1)!*Stirling2(n+2,k+2) (Brenti and Welker). Row sums are A002050. - _Peter Bala_, Jul 12 2014

%e T(2,1) = 12 because there are 12 such length 2 sequences of subsets of {1,2,3}: ({1},{2}), ({1},{3}), ({2},{3}), ({1},{2,3}), ({2},{1,3}), ({3},{1,2}) with two orderings for each. - _Geoffrey Critzer_, Dec 20 2011

%e Triangle begins:

%e    1

%e    3      2

%e    7     12      6

%e   15     50     60     24

%e   31    180    390    360    120

%p with(combinat):

%p a := (n, k) -> (k+1)!*stirling2(n+2, k+2):

%p seq(print(seq(a(n, k), k = 0..n)), n = 0..10);

%t nn = 5; a = Exp[ x] - 1 ; f[list_] := Select[list, # > 0 &];Map[f, Transpose[Table[Drop[Range[0, nn]!CoefficientList[Series[a^k  Exp[x], {x, 0, nn}],x], 1], {k, 1, 5}]]] // Grid (* _Geoffrey Critzer_, Dec 20 2011 *)

%t Table[(k+1)!*StirlingS2[n+2,k+2], {n,0,10}, {k,0,n}]//Flatten (* _G. C. Greubel_, Nov 19 2017 *)

%o (PARI) for(n=0,10, for(k=0,n, print1((k+1)!*stirling(n+2,k+2,2), ", "))) \\ _G. C. Greubel_, Nov 19 2017

%Y Cf. A028246.

%Y Cf. A002050 (row sums), A019538.

%K nonn,easy,tabl,nice

%O 0,2

%A _Rob Arthan_, Jan 12 2000

%E More terms from _James A. Sellers_, Jan 14 2000