a(n) is the least k such that k concatenated with k + n is prime.

Terms

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