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 A083721 #9 Feb 21 2013 00:27:22 %S A083721 0,0,0,1,0,1,0,3,2,1,0,3,0,2,3,5,0,5,0,5,4,3,0,7,6,3,7,5,0,7,0,10,6,4, %T A083721 7,9,0,4,6,9,0,9,0,9,11,5,0,13,11,12,8,9,0,14,11,12,8,6,0,14,0,7,14, %U A083721 17,12,13,0,12,10,15,0,18,0,9,18,13,16,15,0,19,20,9,0,19,16,9,13,18,0,21,18 %N A083721 Number of primes greater than the greatest prime factor of n but not greater than n. %C A083721 a(n) = A000720(n) - A000720(A006530(n)); %C A083721 a(n) > 0 if and only if n is composite. %o A083721 (PARI) a(n)=if(n>3,my(f=factor(n)[,1]);primepi(n)-primepi(f[#f]),0) \\ _Charles R Greathouse IV_, Feb 21 2013 %Y A083721 Cf. A083722, A079067. %K A083721 nonn %O A083721 1,8 %A A083721 _Reinhard Zumkeller_, May 04 2003