Primes that are concatenations of k with k + 4.

Terms

a(0) =37a(1) =59a(2) =1721a(3) =2731a(4) =3539a(5) =3943a(6) =4549a(7) =4751a(8) =6367a(9) =6569a(10) =8387a(11) =9397a(12) =99103a(13) =113117a(14) =123127a(15) =147151a(16) =149153a(17) =173177a(18) =185189a(19) =203207a(20) =209213a(21) =213217a(22) =219223a(23) =227231a(24) =239243a(25) =249253a(26) =255259a(27) =263267a(28) =267271a(29) =285289