a(1)=4. a(n+1) = a(n)+d-1, where d is the smallest prime divisor of (a(n)-1)*(a(n)+1).

Terms

a(0) =4a(1) =6a(2) =10a(3) =12a(4) =22a(5) =24a(6) =28a(7) =30a(8) =58a(9) =60a(10) =118a(11) =120a(12) =126a(13) =130a(14) =132a(15) =138a(16) =274a(17) =276a(18) =280a(19) =282a(20) =562a(21) =564a(22) =568a(23) =570a(24) =1138a(25) =1140a(26) =1146a(27) =1150a(28) =1152a(29) =2302