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 A092993 #12 Oct 20 2014 08:19:28 %S A092993 23,0,53,73,113,13131313133,173,193,233,293,313,373,41413,433, %T A092993 47474747474747474747474747473,53535353535353535353535353533,593,613, %U A092993 673,71713,733,0,83833,89898989893,97973,1013,1033,1071071071073,1093 %N A092993 Smallest prime of the form concatenation(s) of prime(n) with itself followed by a 3, or 0 if no such prime exists. %C A092993 Start with p=prime(n). If concat(p,3) is prime, then this is a(n), else consider concat(p,p,3), and so on. %e A092993 For a(1), start with prime(1)=2. Since appending a digit 3 yields the prime 23, a(1)=23. %e A092993 For a(2), start with prime(2)=3. Since concatenating any number of digits '3' never yields a prime, a(2)=0. %e A092993 For a(6), starting with prime(6)=13, one has to take 5 concatenations of itself before a prime is obtained when a final digit '3' is appended, thus a(6)=13131313133. %e A092993 a(22)=0 since the concatenation of prime(22)=79 with itself, followed by a 3, is always composite. - _Giovanni Resta_, Apr 07 2006 %Y A092993 Cf. A092992, A092994, A092995. %K A092993 base,nonn %O A092993 1,1 %A A092993 _Amarnath Murthy_, Mar 28 2004 %E A092993 a(15)-a(21) from _Stefan Steinerberger_, Nov 09 2005 %E A092993 More terms from _Giovanni Resta_, Apr 07 2006