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 A219029 #38 Sep 08 2022 08:46:04
%S A219029 -1,0,1,2,2,4,4,5,6,7,6,9,8,11,10,11,8,15,12,15,16,17,12,19,16,21,20,
%T A219029 23,16,25,22,23,24,25,26,31,24,31,30,31,24,37,30,35,36,35,24,39,36,41,
%U A219029 34,43,28,47,38,47,44,45,30,51,44,53,50,47,48,57,46,51,48
%N A219029 a(n) = n - 1 - phi(phi(n)).
%C A219029 There are exactly n - 1 - phi(phi(n)) non-primitive roots for n, less than n, if n is prime.
%C A219029 a(n) will be the same as A219027(n) except when n is a member of A033949 or n = 1, i.e., n is not 2, 4, prime, power of a prime, twice a prime, or twice a prime power.
%H A219029 Vincenzo Librandi, <a href="/A219029/b219029.txt">Table of n, a(n) for n = 1..1000</a>
%F A219029 a(n) = n - 1 - A010554(n). - _V. Raman_, Nov 22 2012
%t A219029 Table[n - (EulerPhi[EulerPhi[n]] + 1), {n, 75}] (* _Alonso del Arte_, Nov 17 2012 *)
%o A219029 (PARI) for(n=1,100,print1(n-1-eulerphi(eulerphi(n))","))
%o A219029 (Magma) [(n - 1 - EulerPhi(EulerPhi(n))): n in [1..70] ]; // _Vincenzo Librandi_, Jan 26 2013
%Y A219029 Cf. A008330 (number of primitive roots for the n-th prime).
%Y A219029 Cf. A046144 (number of primitive roots for n).
%Y A219029 Cf. A010554 (value of phi(phi(n))).
%Y A219029 Cf. A219027, A219428.
%K A219029 sign
%O A219029 1,4
%A A219029 _V. Raman_, Nov 10 2012