Number of non-isomorphic n-element sets of singletons or pairs of elements of {1..n} with union {1..n}, or unlabeled loop-graphs with n edges covering n vertices.
A368599
Number of non-isomorphic n-element sets of singletons or pairs of elements of {1..n} with union {1..n}, or unlabeled loop-graphs with n edges covering n vertices.
Terms
- a(0) =1a(1) =1a(2) =2a(3) =5a(4) =13a(5) =34a(6) =97a(7) =277a(8) =825a(9) =2486a(10) =7643a(11) =23772a(12) =74989a(13) =238933a(14) =769488a(15) =2500758a(16) =8199828a(17) =27106647a(18) =90316944a(19) =303182461a(20) =1025139840a(21) =3490606305a(22) =11967066094a(23) =41302863014a(24) =143493606215a(25) =501772078429
External references
- oeis: A368599