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 A176087 #4 May 22 2017 11:58:14 %S A176087 1,253,35473 %N A176087 Numbers n such that (10^n-1)/3 * 10^ceiling(log_10(n+1)) + n is prime. %C A176087 No term is a multiple of 2, 3, or 5. The decimal expansion of each corresponding prime is n 3's with n's decimal expansion concatenated. Probable primes found by PrimeForm. Prime for 253 proved by Primo. No more terms up to 50000. %e A176087 The first term is 1 because 31 is prime. %o A176087 (PARI) is(n)=ispseudoprime((10^n-1)/3 * 10^logint(10*n,10) + n) \\ _Charles R Greathouse IV_, May 22 2017 %Y A176087 Cf. A070746 (n 1's followed by n is prime), A084428 (n 7's followed by n is prime), A174710, A004218. %K A176087 bref,more,nonn %O A176087 1,2 %A A176087 _Rick L. Shepherd_, Apr 08 2010