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 A087604 #7 Dec 05 2013 19:56:32 %S A087604 1,1,0,1,4,0,2,1,0,1,4,0,37,7,0,17,149,0,185,7,0,73,1,0,5,47,0,38,4,0, %T A087604 4,133,0,52,2,0,194,46,0,37,29,0,29,25,0,19,14,0,74,8,0,19,20,0,442, %U A087604 83,0,358,211,0,16,298,0,260,5,0,305,71,0,8,323,0,5,109,0,8,68,0,767,367 %N A087604 Smallest k such that n times concatenation of k with itself followed by a 3 is a prime, or 0 if no such number exists. %C A087604 Trivially a(3n) = 0. Conjecture: no other term is zero. %C A087604 Either a(13)=0 or a(13)>36. This sequence contains no positive multiples of 3. If a(m) is of the form bbb...b (repeated k times) then a(km) <= b. - _Sam Alexander_, Oct 20 2003 %e A087604 a(5) = 4 as 444443 is a prime. but 111113,222223,333333 are not. %Y A087604 Cf. A086920, A087605, A087606, A087607, A087608, A087609, A087610. %K A087604 base,nonn %O A087604 1,5 %A A087604 _Amarnath Murthy_, Sep 18 2003 %E A087604 More terms from _Sam Alexander_, Oct 20 2003 %E A087604 More terms from _Ray G. Opao_, Apr 15 2004 %E A087604 More terms from _David Wasserman_, Jun 16 2005