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 A253968 #19 Jun 13 2017 10:34:13 %S A253968 2,4,6,10,11,18,29,151,920,1456,1716,1915,4148,4403,8005,9600,41945, %T A253968 47238 %N A253968 Numbers n such that (23*10^n - 26)/6 is prime. %e A253968 n = 2, 4, and 6, yield (23*10^n - 26)/6 = 379, 38329, and 3833329, respectively, which are prime. %t A253968 fQ[n_] := PrimeQ[(23*10^n - 26)/6]; Select[ Range@ 10000, fQ] (* _Robert G. Wilson v_, Jan 28 2015 *) %o A253968 (PARI) is(n)=ispseudoprime((23*10^n-26)/6) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A253968 Cf. A254005. %K A253968 nonn,more %O A253968 1,1 %A A253968 _Hans Havermann_, Jan 24 2015