Arises in enumerating iterated point-line configurations.

Terms

a(0) =4a(1) =4a(2) =4a(3) =4a(4) =5a(5) =5a(6) =6a(7) =6a(8) =7a(9) =8a(10) =9a(11) =10a(12) =11a(13) =13a(14) =14a(15) =16a(16) =19a(17) =22a(18) =26a(19) =30a(20) =36a(21) =43a(22) =52a(23) =63a(24) =77a(25) =95a(26) =119a(27) =151a(28) =193a(29) =249