This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A075609 #5 Jan 08 2019 09:12:41 %S A075609 1,3,7,19,13,61,31,37,67,79,103,43,73,127,139,97,151,157,109,199,181, %T A075609 193,163,211,229,223,241,271,277,331,283,397,337,313,307,367,457,421, %U A075609 349,373,379,433,439,409,463,523,487,601,541,547,499,571,673,613,577 %N A075609 a(1) = 1, a(n) = smallest prime number not occurring earlier such that the concatenation a(n-1) and a(n) is a prime. %Y A075609 Cf. A075607, A075608, A075610. %K A075609 base,nonn %O A075609 1,2 %A A075609 _Amarnath Murthy_, Sep 28 2002 %E A075609 More terms from _Michel ten Voorde_ Jun 23 2003