7^n-prevprime(7^n).

Terms

a(0) =2a(1) =2a(2) =6a(3) =2a(4) =20a(5) =6a(6) =2a(7) =2a(8) =6a(9) =8a(10) =44a(11) =2a(12) =36a(13) =32a(14) =2a(15) =24a(16) =36a(17) =50a(18) =92a(19) =18a(20) =6a(21) =32a(22) =86a(23) =60a(24) =6a(25) =50a(26) =12a(27) =2a(28) =186a(29) =18