a(n) = nextprime(6^n)-6^n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =7a(4) =1a(5) =13a(6) =7a(7) =5a(8) =11a(9) =25a(10) =5a(11) =35a(12) =35a(13) =35a(14) =5a(15) =91a(16) =47a(17) =35a(18) =5a(19) =17a(20) =11a(21) =7a(22) =103a(23) =61a(24) =7a(25) =13a(26) =23a(27) =7a(28) =25a(29) =47