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 A121609 #9 Nov 29 2016 17:50:58 %S A121609 22,25,27,32,33,35,52,55,57,72,75,77,112,115,117,132,133,135,172,175, %T A121609 177,192,195,213,217,219,231,232,235,237,243,247,253,259,261,267,273, %U A121609 279,289,292,295,297,312,315,319,323,329,341,343,361,371,372,375,377 %N A121609 Composite numbers that can be written as concatenation of two primes in decimal representation. %C A121609 Subsequence of A066737. %H A121609 Jean-Marc Falcoz, <a href="/A121609/b121609.txt">Table of n, a(n) for n = 1..11140</a> %e A121609 A002808(249) = 315 = 31*10+5 = A000040(11)*10+A000040(3), %e A121609 therefore 315 is a term: a(44) = 315; %e A121609 A002808(252) = 319 = 3*100+19 = A000040(2)*100+A000040(8), %e A121609 therefore 319 is a term: a(45) = 319. %Y A121609 Cf. A121610, A105184, A121608. %K A121609 nonn,base %O A121609 1,1 %A A121609 _Reinhard Zumkeller_, Aug 10 2006