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 A293516 #11 Nov 27 2017 19:20:00 %S A293516 -1,-1,0,0,0,0,2,0,2,0,2,0,4,2,0,0,0,2,6,0,4,2,2,0,4,4,6,4,4,0,14,0,4, %T A293516 0,8,4,12,6,8,0,8,4,18,4,8,2,2,0,18,4,0,8,4,6,8,8,12,4,2,0,28,14,12,0, %U A293516 16,4,26,0,4,8,22,8,24,12,8,12,28,8,30,0,18,8,2,8,0,18,8,8,8,8,24,4,28,2,24,0,32 %N A293516 a(n) = phi(n) - 2*phi(phi(n)), where phi = Euler totient function, A000010. %H A293516 Antti Karttunen, <a href="/A293516/b293516.txt">Table of n, a(n) for n = 1..65537</a> %F A293516 a(n) = A000010(n) - 2*A010554(n). %F A293516 a(n) = A070556(n) - A010554(n). %F A293516 a(n) = -A083254(A000010(n)). %o A293516 (PARI) A293516(n) = (eulerphi(n) - 2*eulerphi(eulerphi(n))); %Y A293516 Cf. A000010, A010554, A051953, A070556, A083254, A295660. %Y A293516 Cf. A003401 (gives the positions of zeros after the two initial -1's). %K A293516 sign %O A293516 1,7 %A A293516 _Antti Karttunen_, Nov 27 2017