A332908 Number of entries in the fourth cycles of all permutations of [n] when cycles are ordered by increasing lengths.

1, 21, 226, 2612, 29261, 346453, 4338214, 57819554, 815225643, 12234293579, 194294281572, 3264124624256, 57826690252441, 1079032037759257, 21142347350725466, 434563256137908638, 9344589765620199919, 209952915324112384719, 4919186923210370523448

Offset

4,2

Links

Alois P. Heinz, Table of n, a(n) for n = 4..450

Andrew V. Sills, Integer Partitions Probability Distributions, arXiv:1912.05306 [math.CO], 2019.

Wikipedia, Permutation

Maple

b:= proc(n, i, t) option remember; `if`(n=0, [1, 0], `if`(i>n, 0,
      add((p-> p+`if`(t>0 and t-j<1, [0, p[1]*i], 0))((i-1)!^j*
        b(n-i*j, i+1, max(0, t-j))/j!*combinat[multinomial]
         (n, i$j, n-i*j)), j=0..n/i)))
    end:
a:= n-> b(n, 1, 4)[2]:
seq(a(n), n=4..22);

Mathematica

multinomial[n_, k_List] := n!/Times @@ (k!);
b[n_, i_, t_] := b[n, i, t] = If[n == 0, {1, 0}, If[i > n, 0, Sum[Function[ p, p + If[p =!= 0 && t>0 && t - j < 1, {0, p[[1]]*i}, {0, 0}]][(i-1)!^j* b[n - i*j, i + 1, Max[0, t - j]]/j!*multinomial[n, Append[Array[i&, j], n - i*j]]], {j, 0, n/i}]]];
a[n_] := b[n, 1, 4][[2]];
a /@ Range[4, 22] (* Jean-François Alcover, Apr 21 2020, after Alois P. Heinz *)

Crossrefs

Column k=4 of A322383.

Sequence in context: A219439 A219140 A231513 * A027508 A221037 A221500

Adjacent sequences: A332905 A332906 A332907 * A332909 A332910 A332911

Keyword

nonn

Author

Alois P. Heinz, Mar 02 2020

Status

approved