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 A174213 #6 Jan 17 2019 16:53:42 %S A174213 6,8,9,23,29,30,32,39,42,45,53,57,65,80,92,95,101,102,108,113,116,128, %T A174213 141,144,153,161,182,183,186,200,206,216,218,219,225,239,245,249,260, %U A174213 266,270,273,279,281,282,296,311,314,318,321 %N A174213 Natural numbers n such that the concatenation n//1331 is a prime number. %C A174213 n is no multiple of 11 as 1331 = 11^3. %C A174213 Necessarily n = 3 * k or n = 3 * k + 2, but not n = 3 * k + 1, because sod(1331) = 8. %C A174213 Sequence is infinite, Dirichlet's prime number theorem for naturals of the form n * 10^4 + 1331. %C A174213 For prefixed 1331 and references see A173836. %e A174213 61331 = prime(6169) => a(1) = 6. %e A174213 81331 = prime(7958) => a(2) = 8. %t A174213 Select[Range[400],PrimeQ[#*10^4+1331]&] (* _Harvey P. Dale_, Jan 17 2019 *) %o A174213 (PARI) isok(n) = isprime(n*10^4 + 1331); \\ _Michel Marcus_, Aug 27 2013 %Y A174213 A168327, A168417, A173836 %K A174213 base,nonn %O A174213 1,1 %A A174213 Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Mar 12 2010