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 A072731 #8 Feb 20 2025 19:51:54 %S A072731 0,-1,-2,-1,-2,-1,-2,-1,0,1,0,1,0,1,2,3,2,3,2,3,4,5,4,5,6,7,8,9,8,9,8, %T A072731 9,10,11,12,13,12,13,14,15,14,15,14,15,16,17,16,17,18,19,20,21,20,21, %U A072731 22,23,24,25,24,25,24,25,26,27,28,29,28,29,30,31,30,31,30,31,32,33,34 %N A072731 Difference of numbers of composite and prime numbers <= n. %C A072731 a(n+1) = a(n) + A066247(n) - A010051(n), a(1) = 0. %C A072731 a(n) < 0 iff 1 < n <= 8. %F A072731 a(n) = A065855(n) - A000720(n). %F A072731 a(n) = n - 2*pi(n) - 1. - _Wesley Ivan Hurt_, Jun 16 2013 %Y A072731 Cf. A000040, A000720 (pi), A002808, A010051, A065855, A066247. %K A072731 sign %O A072731 1,3 %A A072731 _Reinhard Zumkeller_, Aug 08 2002