login
A327702
Number of refinement sequences n -> ... -> {1}^n, where in each step one part that is the rightmost copy of its size is replaced by a partition of itself into smaller parts (in weakly decreasing order).
5
1, 1, 2, 5, 14, 47, 174, 730, 3300, 16361, 85991, 485982, 2877194, 18064663, 118111993, 810388956, 5755059363, 42643884970, 325468477721, 2576976440845, 20960795772211, 176056148076418, 1514733658531058, 13418942409623726, 121442280888373117, 1128425823360525506
OFFSET
1,3
EXAMPLE
a(4) = 5:
4 -> 1111
4 -> 211 -> 1111
4 -> 31 -> 1111
4 -> 31 -> 211 -> 1111
4 -> 22 -> 211 -> 1111
MAPLE
v:= l-> [seq(`if`(i=1 or l[i]>l[i-1], seq(subs(1=[][], sort(
subsop(i=h[], l))), h=({combinat[partition](l[i])[]}
minus{[l[i]]})), [][]), i=1..nops(l))]:
b:= proc(l) option remember; `if`(max(l)<2, 1, add(b(h), h=v(l))) end:
a:= n-> b([n]):
seq(a(n), n=1..26);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Sep 22 2019
STATUS
approved