OFFSET
0,3
EXAMPLE
The a(3) = 6 ordered set partitions: (123), (1)(23), (2)(13), (12)(3), (3)(12), (1)(2)(3).
MATHEMATICA
sps[{}]:={{}}; sps[set:{i_, ___}]:=Join@@Function[s, Prepend[#, s]&/@sps[Complement[set, s]]]/@Cases[Subsets[set], {i, ___}];
Table[Sum[Times@@Factorial/@Length/@GatherBy[sptn, Total], {sptn, sps[Range[n]]}], {n, 8}]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Mar 03 2018
EXTENSIONS
a(12)-a(15) from Alois P. Heinz, Mar 03 2018
a(16)-a(22) from Christian Sievers, Aug 30 2024
STATUS
approved