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 A260880 #8 Aug 18 2015 12:27:32 %S A260880 1,1,9,7,3,3,37,7,7,19,3,37,31,37,61,13,3,3,39,139,57,9,49,7,67,331, %T A260880 319,211,57,33,49,61,103,69,67,43,321,37,3,169,63,57,31,121,9,33,217, %U A260880 69,9,327,171,157,31,21,279,3,193,19,67,7,121,399,57,49,49,49 %N A260880 Smallest k such that 1000...0//k (concatenation of 10^n and k) is prime. %H A260880 Felix Fröhlich, <a href="/A260880/b260880.txt">Table of n, a(n) for n = 0..1000</a> %e A260880 The smallest prime whose decimal expansion starts with 10^6 = 1000000 is 100000037, so a(6) = 37. %o A260880 (PARI) a(n) = my(k=1); while(!ispseudoprime(eval(Str(10^n, k))), k++); k %Y A260880 Similar to but different from A033873. %K A260880 nonn,base %O A260880 0,3 %A A260880 _Felix Fröhlich_, Aug 02 2015