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 A072106 #14 Nov 07 2024 08:47:06
%S A072106 0,0,0,1,1,1,2,3,2,3,4,3,5,5,4,7,8,5,9,7,5,9,11,7,10,11,10,11,15,7,16,
%T A072106 15,11,15,13,11,20,17,14,15,23,11,24,19,15,21,26,15,23,19,19,23,30,17,
%U A072106 23,23,21,27,33,15,34,29,22,31,27,19,38,31,28,23,41,23,42,35,26,35,37
%N A072106 The number of nontotients (even and odd) in the reduced residue system of n.
%H A072106 Amiram Eldar, <a href="/A072106/b072106.txt">Table of n, a(n) for n = 1..10000</a>
%e A072106 For n=113: the reduced residue system consists of 112 numbers: Card[OddNonTotients(113)] = 56 - 1, EvenNonTotients = {14,26,34,38,50,62,68,74,76,86,90,94,98}, i.e., 13 terms, therefore a(113) = 56 - 1 + 13 = 68.
%o A072106 (PARI) a(n) = sum(k = 1, n, gcd(n, k) == 1 && !istotient(k)); \\ _Amiram Eldar_, Nov 07 2024
%Y A072106 Cf. A000010, A002202, A005277, A037225, A072451, A072455.
%K A072106 nonn
%O A072106 1,7
%A A072106 _Labos Elemer_, Jun 19 2002