Number of line graphs on n unlabeled nodes.

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =24a(5) =63a(6) =166a(7) =471a(8) =1408a(9) =4436a(10) =14719a(11) =51468a(12) =188754a(13) =725010a(14) =2907576a(15) =12141462a(16) =52654529a(17) =236584104a(18) =1098926868a(19) =5266708497a(20) =25997964452a(21) =131975740172a(22) =688019138485