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 A233464 #15 Mar 16 2014 10:59:51
%S A233464 1,19,5641,1289743,2578966671
%N A233464 a(n) is the smallest natural number m such that 10^10^k + m is prime for k = 0, 1, ...., n.
%e A233464 29 (=10^1+19) and 10000000019 (=10^10+19) are primes so a(1)=19.
%o A233464 (PARI) okm(m, n) = {for (k=0, n, if (!isprime(10^10^k + m), return (0)););return (1);}
%o A233464 a(n) = {m = 0; while (!okm(m, n), m++); m;} \\ _Michel Marcus_, Mar 16 2014
%Y A233464 Cf. A129613, A129614, A129615.
%K A233464 nonn,hard,more
%O A233464 0,2
%A A233464 _Farideh Firoozbakht_, Mar 13 2014
%E A233464 a(4) from _Giovanni Resta_, Mar 14 2014