a(1) = 1. If a(n) is prime, a(n+1) = 2*a(n); otherwise, a(n+1) = 2*a(n) + 1.

Terms

a(0) =1a(1) =3a(2) =6a(3) =13a(4) =26a(5) =53a(6) =106a(7) =213a(8) =427a(9) =855a(10) =1711a(11) =3423a(12) =6847a(13) =13695a(14) =27391a(15) =54783a(16) =109567a(17) =219134a(18) =438269a(19) =876539a(20) =1753079a(21) =3506159a(22) =7012318a(23) =14024637a(24) =28049275a(25) =56098551a(26) =112197103a(27) =224394207a(28) =448788415a(29) =897576831