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 A086920 #6 Dec 05 2013 19:56:20 %S A086920 1,3,2,3,3,3,3,30,6,4,5,5,25,42,17,19,2,1,7,6,6,1,50,29,138,153,4,45, %T A086920 54,7,15,9,78,147,95,58,102,18,3,115,54,6,46,9,24,64,183,120,3,33,112, %U A086920 46,105,4,279,122,68,75,3,22,294,56,92,76,6,19,94,71,12,75,30,16,78,320,33 %N A086920 Smallest k such that n times concatenation of k with itself followed by a 1 is a prime, or 0 if no such number exists. %C A086920 Conjecture: no term is zero. %e A086920 a(3) = 2 as 2221 is a prime. a(4) = 3 as 33331 is a prime but 11111 and 22221 are not. %e A086920 a(8) = 30 and the prime arising is 30303030303030301. %Y A086920 Cf. A087604, A087605, A087606, A087607, A087608, A087609. %Y A086920 Cf. A086923. %Y A086920 Cf. A086766. %K A086920 base,nonn %O A086920 1,2 %A A086920 _Amarnath Murthy_, Sep 18 2003 %E A086920 More terms from _Ray G. Opao_, Apr 15 2004 %E A086920 More terms from _David Wasserman_, Apr 12 2005