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 A139368 #11 Oct 03 2015 23:19:48 %S A139368 1,2,1,2,1,1,3,3,5,4,5,5,3,2,1,1,2,7,8,7,7,4,6,6,3,5,6,6,6,8,6,8,4,6, %T A139368 4,9,9,9,10,11,12,10,11,10,12,16,9,9,9,5,8,7,5,7,8,13,11,6,7,5,1,1,2, %U A139368 10,11,15,15,14,12,10,12,9,9,14,18,13,14,13,14,14,12,8,8,8,7,8,4,6,7,11,10 %N A139368 a(n) = A024912(n) - A102342(n). %C A139368 A139368(219) = -4. %H A139368 <a href="/index/Pri#prime_races">Index entries for prime races</a> %p A139368 From _R. J. Mathar_, Apr 25 2010: (Start) %p A139368 A102342 := proc(n) option remember; if n = 1 then 0; else for a from procname(n-1)+1 do if isprime(10*a+7) then return a; end if; end do: end if; end proc: %p A139368 A024912 := proc(n) option remember; if n = 1 then 1; else for a from procname(n-1)+1 do if isprime(10*a+1) then return a; end if; end do: end if; end proc: %p A139368 A139368 := proc(n) A024912(n)-A102342(n) ; end proc: seq(A139368(n),n=1..120) ; (End) %K A139368 sign %O A139368 1,2 %A A139368 _Juri-Stepan Gerasimov_, Jun 09 2008 %E A139368 More terms from _R. J. Mathar_, Apr 25 2010