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 A075608 #5 Jan 08 2019 09:12:41 %S A075608 1,9,77,27,49,33,91,51,133,39,119,69,143,21,121,57,203,93,169,63,247, %T A075608 81,299,147,209,123,217,87,187,111,253,153,259,99,289,129,221,159,161, %U A075608 141,301,177,319,117,329,201,287,219,361,183,343,237,581,171,341,273,323 %N A075608 a(1) = 1, a(n) = smallest composite number not occurring earlier such that the concatenation a(n-1) and a(n) is a prime. %Y A075608 Cf. A075607, A075609, A075610. %K A075608 base,nonn %O A075608 1,2 %A A075608 _Amarnath Murthy_, Sep 28 2002 %E A075608 More terms from _Michel ten Voorde_ Jun 23 2003