Number of 4-indecomposable (connected) graphs on n nodes.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =6a(5) =21a(6) =112a(7) =853a(8) =111a(9) =181a(10) =323a(11) =437a(12) =717a(13) =1198a(14) =1606a(15) =2454a(16) =3782a(17) =4997a(18) =7245a(19) =10543a(20) =13711a(21) =19092a(22) =26612a(23) =34076a(24) =45948a(25) =61930a(26) =78154a(27) =102654a(28) =134670a(29) =167688