a(0)=0; for n > 0, a(n) = 2*a(n-1) if n-1 is prime, a(n-1) + 1 otherwise.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =8a(5) =9a(6) =18a(7) =19a(8) =38a(9) =39a(10) =40a(11) =41a(12) =82a(13) =83a(14) =166a(15) =167a(16) =168a(17) =169a(18) =338a(19) =339a(20) =678a(21) =679a(22) =680a(23) =681a(24) =1362a(25) =1363a(26) =1364a(27) =1365a(28) =1366a(29) =1367