Number of connected functions (or mapping patterns) on n unlabeled points, or number of rings and branches with n edges.

A002861

Number of connected functions (or mapping patterns) on n unlabeled points, or number of rings and branches with n edges.

Terms

    a(0) =1a(1) =2a(2) =4a(3) =9a(4) =20a(5) =51a(6) =125a(7) =329a(8) =862a(9) =2311a(10) =6217a(11) =16949a(12) =46350a(13) =127714a(14) =353272a(15) =981753a(16) =2737539a(17) =7659789a(18) =21492286a(19) =60466130a(20) =170510030a(21) =481867683a(22) =1364424829a(23) =3870373826a(24) =10996890237a(25) =31293083540a(26) =89173833915a(27) =254445242754a(28) =726907585652

External references