Concatenations of pairs of primes that differ by four.

Terms

a(0) =37a(1) =711a(2) =1317a(3) =1923a(4) =3741a(5) =4347a(6) =6771a(7) =7983a(8) =97101a(9) =103107a(10) =109113a(11) =127131a(12) =163167a(13) =193197a(14) =223227a(15) =229233a(16) =277281a(17) =307311a(18) =313317a(19) =349353a(20) =379383a(21) =397401a(22) =439443a(23) =457461a(24) =463467a(25) =487491a(26) =499503a(27) =613617a(28) =643647a(29) =673677