a(n) is the least k such that (10^k)*Mersenne-prime(n) + 1 is prime.

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =2a(5) =3a(6) =10a(7) =6a(8) =28a(9) =12a(10) =45a(11) =23a(12) =36a(13) =18a(14) =114a(15) =72a(16) =652a(17) =47a(18) =39a(19) =61a(20) =3713a(21) =208a(22) =9655a(23) =965a(24) =11508a(25) =684a(26) =7085a(27) =1803