Number of non-isomorphic n-element sets of singletons or pairs of elements of {1..n}, or unlabeled loop-graphs with n edges and up to n vertices.
A368598
Number of non-isomorphic n-element sets of singletons or pairs of elements of {1..n}, or unlabeled loop-graphs with n edges and up to n vertices.
Terms
- a(0) =1a(1) =1a(2) =2a(3) =6a(4) =17a(5) =52a(6) =173a(7) =585a(8) =2064a(9) =7520a(10) =28265a(11) =109501a(12) =437394a(13) =1799843a(14) =7629463a(15) =33302834a(16) =149633151a(17) =691702799a(18) =3287804961a(19) =16058229900a(20) =80533510224a(21) =414384339438
External references
- oeis: A368598