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 A073256 #22 Jun 03 2025 02:27:29
%S A073256 2,2,4,6,4,4,6,8,8,6,8,12,10,8,20,12,18,12,8,16,20,16,24,12,18,24,16,
%T A073256 12,20,24,22,16,42,20,32,24,18,40,24,36,28,16,30,36,32,48,20,32,44,24,
%U A073256 24,36,40,36,60,24,32,54,40,24,64,42,56,40,24,72,44,60,46,72,32,42,60
%N A073256 a(n) = phi(n-th composite number).
%H A073256 Vincenzo Librandi, <a href="/A073256/b073256.txt">Table of n, a(n) for n = 1..1200</a>
%F A073256 a(n) = A000010(A002808(n)).
%e A073256 100th composite is 133; phi(133) = 108 = a(100).
%t A073256 c[x_] := FixedPoint[x+PrimePi[ # ]+1&, x]; Table[EulerPhi[c[w]], {w, 1, 128}]
%t A073256 With[{nn=100},EulerPhi[#]&/@Complement[Range[2,nn], Prime[Range[ PrimePi[ nn]]]]] (* _Harvey P. Dale_, Apr 28 2014 *)
%t A073256 EulerPhi[Select[Range[100],CompositeQ]] (* _Harvey P. Dale_, Jul 05 2024 *)
%Y A073256 Cf. A000010, A002808, A035004, A073255.
%K A073256 nonn
%O A073256 1,1
%A A073256 _Labos Elemer_, Jul 22 2002