Primes formed by concatenating k and 2k+1.

Terms

a(0) =13a(1) =37a(2) =613a(3) =919a(4) =1021a(5) =1123a(6) =1327a(7) =1429a(8) =1531a(9) =2143a(10) =2347a(11) =2551a(12) =2857a(13) =3061a(14) =3163a(15) =3469a(16) =3571a(17) =3673a(18) =3877a(19) =4591a(20) =4999a(21) =50101a(22) =56113a(23) =59119a(24) =63127a(25) =70141a(26) =71143a(27) =74149a(28) =78157a(29) =79159