OFFSET
2,4
COMMENTS
Row n counts even signed permutations w in D_n such that (i.) w(1) != -n and (ii.) all right-to-left maxima of |w| are negative in w, by their type D descent number. For example, T(3,2) = 4 counts the signed permutations (1,-3,-2), (-2,1,-3), (2,-1,-3), (2,-3,-1).
LINKS
Jose Bastidas, Table of n, a(n) for n = 2..1225
J. Bastidas, C. Hohlweg and F. Saliola, The Primitive Eulerian polynomial, arXiv:2306.15556 [math.CO], 2023. Table 3.
EXAMPLE
0, 1;
1, 4, 1;
4, 20, 20, 1;
11, 116, 216, 76, 1;
26, 632, 2072, 1732, 262, 1;
57, 3158, 18404, 28064, 11824, 862, 1;
120, 14800, 151104, 386640, 317200, 73320, 2760, 1;
...
CROSSREFS
KEYWORD
nonn,tabf
AUTHOR
Jose Bastidas, Jun 28 2023
STATUS
approved