A111492 Triangle read by rows: a(n,k) = (k-1)! * C(n,k).

1, 2, 1, 3, 3, 2, 4, 6, 8, 6, 5, 10, 20, 30, 24, 6, 15, 40, 90, 144, 120, 7, 21, 70, 210, 504, 840, 720, 8, 28, 112, 420, 1344, 3360, 5760, 5040, 9, 36, 168, 756, 3024, 10080, 25920, 45360, 40320, 10, 45, 240, 1260, 6048, 25200, 86400, 226800, 403200, 362880

Offset: 1

Author

Ross La Haye, Nov 15 2005

Keywords

• nonn
• tabl

Comments

For k > 1, a(n,k) = the number of permutations of the symmetric group S_n that are pure k-cycles.

Reverse signed array is A238363. For a relation to (Cauchy-Euler) derivatives of the Vandermonde determinant, see Chervov link. - Tom Copeland, Apr 10 2014

Dividing the k-th column of T by (k-1)! for each column generates A135278 (the f-vectors, or face-vectors for the n-simplices). Then ignoring the first column gives A104712, so T acting on the column vector (-0,d,-d^2/2!,d^3/3!,...) gives the Euler classes for hypersurfaces of degree d in CP^n. Cf. A104712 and Dugger link therein. - Tom Copeland, Apr 11 2014

With initial i,j,n=1, given the n X n Vandermonde matrix V_n(x_1,...,x_n) with elements a(i=row,j=column)=(x_j)^(i-1), its determinant |V_n|, and the column vector of n ones C=(1,1,...,1), the n-th row of the lower triangular matrix T is given by the column vector determined by (1/|V_n|) * V_n(:x_1*d/dx_1:,...,:x_n*d/dx_n:)|V_n| * C, where :x_j*d/dx_j:^n = (x_j)^n*(d/dx_j)^n. - Tom Copeland, May 20 2014

For some other combinatorial interpretations of the first three columns of T, see A208535 and the link to necklace polynomials therein. Because of the simple relation of the array to the Pascal triangle, it can easily be related to many other arrays, e.g., T(p,k)/(p*(k-1)!) with p prime gives the prime rows of A185158 and A051168 when the non-integers are rounded to 0. - Tom Copeland, Oct 23 2014

Examples

			a(3,3) = 2 because (3-1)!C(3,3) = 2.
1;
2 1;
3 3 2;
4 6 8 6;
5 10 20 30 24;
6 15 40 90 144 120;
7 21 70 210 504 840 720;
8 28 112 420 1344 3360 5760 5040;
9 36 168 756 3024 10080 25920 45360 40320;
		

Links

• A. Chervov, A sum involving derivatives of Vandermonde

Programs

Magma

/* As triangle: */ [[Factorial(k-1)*Binomial(n,k): k in [1..n]]: n in [1.. 15]]; // Vincenzo Librandi, Oct 21 2014

Mathematica

Flatten[Table[(k - 1)!Binomial[n, k], {n, 10}, {k, n}]]

Formula

a(n, k) = (k-1)!C(n, k) = P(n, k)/k.

E.g.f. (by columns) = exp(x)((x^k)/k).

a(n, 1) = A000027(n);

a(n, 2) = A000217(n-1);

a(n, 3) = A007290(n);

a(n, 4) = A033487(n-3).

a(n, n) = A000142(n-1);

a(n, n-1) = A001048(n-1) for n > 1.

Sum[a(n, k), {k, 1, n}] = A002104(n);

Sum[a(n, k), {k, 2, n}] = A006231(n).

a(n,k) = sum(j=k..n-1, j!/(j-k)!) (cf. Chervov link). - Tom Copeland, Apr 10 2014

From Tom Copeland, Apr 28 2014: (Start)

E.g.f. by row: [(1+t)^n-1]/t.

E.g.f. of row e.g.f.s: {exp[(1+t)*x]-exp(x)}/t.

O.g.f. of row e.g.f.s: {1/[1-(1+t)*x] - 1/(1-x)}/t.

E.g.f. of row o.g.f.s: -exp(x) * log(1-t*x). (End)