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 A111479 #7 Dec 05 2013 19:57:05
%S A111479 2,1,4,11,3,617,96,1213,1965
%N A111479 a(n) = least positive number such that (2 Concat Concat_{k=1}^n Repeat(A045572(n), a(n))) is a prime. A045572 = odd numbers not divisible by 5.
%C A111479 Concat is the operator that concatenates two numbers as decimal strings and Repeat returns the number obtained by concatenating the first argument to itself the second argument number of times.
%e A111479 21 is not a prime, but 211 is, so a(1)=2.
%e A111479 211,2113,21137777 are all primes. 21137777 is a prime obtained as 2 followed by two 1's, one 3 and four 7's, so a(2) = 4.
%Y A111479 Cf. A111471, A111472, A111473, A111475, A111477, A111478, A111480.
%K A111479 base,more,nonn,less
%O A111479 1,1
%A A111479 _Amarnath Murthy_, Aug 05 2005
%E A111479 Edited by _Franklin T. Adams-Watters_, Aug 29 2006.
%E A111479 Corrected and extended by _Max Alekseyev_, May 21 2009