a(n) = 2*a(n-1) + 1 for a(n-1) not prime, otherwise a(n) = prime(n) - 1; with a(1)=1.

Terms

a(0) =1a(1) =3a(2) =4a(3) =9a(4) =19a(5) =12a(6) =25a(7) =51a(8) =103a(9) =28a(10) =57a(11) =115a(12) =231a(13) =463a(14) =46a(15) =93a(16) =187a(17) =375a(18) =751a(19) =70a(20) =141a(21) =283a(22) =82a(23) =165a(24) =331a(25) =100a(26) =201a(27) =403a(28) =807a(29) =1615