Number of graphs with loops (symmetric relations) with n edges.

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =38a(5) =107a(6) =318a(7) =972a(8) =3111a(9) =10410a(10) =36371a(11) =132656a(12) =504636a(13) =1998361a(14) =8224448a(15) =35112342a(16) =155211522a(17) =709123787a(18) =3342875421a(19) =16234342515a(20) =81102926848a(21) =416244824068