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 A260874 #7 Aug 18 2015 12:25:52 %S A260874 1331133113, %T A260874 17711771177117711771177117711771177117711771177117711771177117711771177117, %U A260874 19911991199119,23322332233223322332233223322332233223322332233223322332233223322332233223322332233223322332233223322332233223322332233223,2992299229,31133113311331 %N A260874 Smallest prime of the form p//r//p//r//p//r// ...., where p = prime(n), r = A004086(p) and // denotes concatenation. %H A260874 Felix Fröhlich, <a href="/A260874/b260874.txt">Table of n, a(n) for n = 6..100</a> %o A260874 (PARI) a(n) = p=prime(n); r=eval(concat(Vecrev(Str(p)))); s=eval(Str(p, r)); i=0; while(!ispseudoprime(s), if(i%2==0, s=eval(Str(s, p)); i++, s=eval(Str(s, r)); i++)); s %Y A260874 Cf. A067087, A110408. %K A260874 nonn,base %O A260874 6,1 %A A260874 _Felix Fröhlich_, Aug 02 2015