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 A318840 #6 Sep 12 2018 10:49:09
%S A318840 0,0,0,1,0,1,0,3,4,3,0,3,0,5,4,7,0,5,0,7,8,9,0,7,16,11,16,9,0,7,0,15,
%T A318840 16,15,20,11,0,17,20,15,0,11,0,19,16,21,0,15,36,19,28,21,0,17,36,23,
%U A318840 32,27,0,15,0,29,32,31,32,15,0,31,40,21,0,23,0,35,36,33,56,23,0,31,52,39,0,23,48,41,52,39,0,23,36,43,56,45,68,31
%N A318840 a(n) = phi(n) - Product_{primes p dividing n} gcd(p-1, n-1).
%H A318840 Antti Karttunen, <a href="/A318840/b318840.txt">Table of n, a(n) for n = 1..65537</a>
%F A318840 a(n) = A000010(n) - A063994(n).
%F A318840 a(n) = A318828(n) - A051953(n).
%o A318840 (PARI)
%o A318840 A063994(n) = { my(f=factor(n)[,1]); prod(i=1, #f, gcd(f[i]-1, n-1)); };
%o A318840 A318840(n) = (eulerphi(n) - A063994(n));
%Y A318840 Cf. A000010, A063994, A318828, A318830.
%K A318840 nonn
%O A318840 1,8
%A A318840 _Antti Karttunen_, Sep 11 2018