OFFSET
0,3
COMMENTS
Row-sums of left portion of A369199.
FORMULA
Inverse binomial transform of A369196.
EXAMPLE
The a(0) = 1 through a(3) = 23 loop-graphs (loops shown as singletons):
{} {{1}} {{1,2}} {{1},{2,3}}
{{1},{2}} {{2},{1,3}}
{{1},{1,2}} {{3},{1,2}}
{{2},{1,2}} {{1,2},{1,3}}
{{1,2},{2,3}}
{{1},{2},{3}}
{{1,3},{2,3}}
{{1},{2},{1,3}}
{{1},{2},{2,3}}
{{1},{3},{1,2}}
{{1},{3},{2,3}}
{{2},{3},{1,2}}
{{2},{3},{1,3}}
{{1},{1,2},{1,3}}
{{1},{1,2},{2,3}}
{{1},{1,3},{2,3}}
{{2},{1,2},{1,3}}
{{2},{1,2},{2,3}}
{{2},{1,3},{2,3}}
{{3},{1,2},{1,3}}
{{3},{1,2},{2,3}}
{{3},{1,3},{2,3}}
{{1,2},{1,3},{2,3}}
MATHEMATICA
Table[Length[Select[Subsets[Subsets[Range[n], {1, 2}]], Length[Union@@#]==n&&Length[#]<=n&]], {n, 0, 5}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 17 2024
STATUS
approved