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 A261455 #11 Aug 21 2015 02:04:26 %S A261455 2,4,13,30,73,82,120,168,227,422,433,451,607,612,798,1527,6958 %N A261455 Numbers n such that 1+131*10^(n-1)+100^n is prime. %C A261455 No other terms < 10000. %e A261455 For n=2, 11311 is prime. %e A261455 For n=3, 1013101 is not prime. %e A261455 For n=4, 100131001 is prime. %o A261455 (PARI) isok(n)=isprime(1+131*10^(n-1)+100^n) \\ _Anders Hellström_, Aug 20 2015 %Y A261455 Cf. A171411, A171376. %K A261455 nonn,more %O A261455 1,1 %A A261455 _Chai Wah Wu_, Aug 20 2015