a(1)=2; for n>1, a(n)=2*a(n-1)-1 if that number is composite, a(n)=a(n-1)+1 otherwise.

Terms

a(0) =2a(1) =3a(2) =4a(3) =5a(4) =9a(5) =10a(6) =11a(7) =21a(8) =22a(9) =23a(10) =45a(11) =46a(12) =91a(13) =92a(14) =183a(15) =365a(16) =729a(17) =1457a(18) =2913a(19) =5825a(20) =11649a(21) =11650a(22) =23299a(23) =46597a(24) =93193a(25) =186385a(26) =186386a(27) =372771a(28) =745541a(29) =1491081