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 A048983 #8 Oct 25 2019 21:20:26
%S A048983 0,0,0,2,1,0,1,3,2,0,1,5,3,0,11,4,9,4,0,5,10,6,14,2,7,13,5,1,7,11,9,2,
%T A048983 27,6,18,10,3,25,9,21,13,1,13,19,14,31,4,14,26,7,5,16,20,16,40,5,11,
%U A048983 32,19,3,42,20,34,18,2,49,21,37,23,49,9,18
%N A048983 As n runs through composite numbers, a(n) = number of composite d < n such that gcd(d,n) = 1.
%F A048983 a(n) = A048984(n) - 1. _Michel Marcus_, Jul 14 2013
%e A048983 9 is 4th composite number, gcd(9,4) = gcd(9,8) = 1, so a(4) = 2.
%o A048983 (PARI) lista(nn) = {forcomposite (n=1, nn, nb = 0; forcomposite(d=1, n-1, if (gcd(n, d) == 1, nb++)); print1(nb, ", "););} \\ _Michel Marcus_, Jul 14 2013
%Y A048983 Cf. A000010, A048984, A002808.
%K A048983 easy,nonn
%O A048983 1,4
%A A048983 _Naohiro Nomoto_