Primes formed by concatenating k with k-1.

Terms

a(0) =43a(1) =109a(2) =2221a(3) =2423a(4) =3433a(5) =4241a(6) =5857a(7) =7069a(8) =7877a(9) =8887a(10) =10099a(11) =102101a(12) =108107a(13) =112111a(14) =114113a(15) =124123a(16) =148147a(17) =154153a(18) =160159a(19) =172171a(20) =180179a(21) =192191a(22) =198197a(23) =202201a(24) =208207a(25) =210209a(26) =214213a(27) =238237a(28) =244243a(29) =262261