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 A219027 #21 Nov 30 2012 14:10:26 %S A219027 0,0,1,2,2,4,4,7,6,7,6,11,8,11,14,15,8,15,12,19,20,17,12,23,16,21,20, %T A219027 27,16,29,22,31,32,25,34,35,24,31,38,39,24,41,30,43,44,35,24,47,36,41, %U A219027 50,51,28,47,54,55,56,45,30,59,44,53,62,63,64,65,46,67,68 %N A219027 Number of non-primitive roots for n, less than n. %C A219027 a(n) will be the same as A219029(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. In such cases, when n is a member of A033949, then a(n) = n-1. %F A219027 n-1-A046144(n). %o A219027 (PARI) for(i=1,100,p=0;for(q=1,i-1,if(gcd(q,i)>1||znorder(Mod(q,i))!=eulerphi(i),p++));print1(p",")) %Y A219027 Cf. A008330 (number of primitive roots for the n-th prime, less than n-th prime). %Y A219027 Cf. A046144 (number of primitive roots for n, less than n). %Y A219027 Cf. A010554 (value of phi(phi(n))). %Y A219027 Cf. A219029. %K A219027 nonn %O A219027 1,4 %A A219027 _V. Raman_, Nov 10 2012