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 A063740 #25 Apr 08 2023 05:02:36
%S A063740 1,1,2,1,1,2,3,2,0,2,3,2,1,2,3,3,1,3,1,3,1,4,4,3,0,4,1,4,3,3,4,3,0,5,
%T A063740 2,2,1,4,1,5,1,4,2,4,2,6,5,5,0,3,0,6,2,4,2,5,0,7,4,3,1,8,4,6,1,3,1,5,
%U A063740 2,7,3,5,1,7,1,8,1,5,2,6,1,9,2,6,0,4,2,10,2,4,2,5,2,7,5,4,1,8,0,9,1,6,1,7
%N A063740 Number of integers k such that cototient(k) = n.
%C A063740 Note that a(0) is also well-defined to be 1 because the only solution to x - phi(x) = 0 is x = 1. - _Jianing Song_, Dec 25 2018
%H A063740 T. D. Noe, <a href="/A063740/b063740.txt">Table of n, a(n) for n = 2..10000</a>
%F A063740 From _Amiram Eldar_, Apr 08 2023 (Start)
%F A063740 a(A005278(n)) = 0.
%F A063740 a(A131825(n)) = 1.
%F A063740 a(A063741(n)) = n. (End)
%e A063740 Cototient(x) = 101 for x in {485, 1157, 1577, 1817, 2117, 2201, 2501, 2537, 10201}, with a(101) = 8 terms; e.g. 485 - phi(485) = 485 - 384 = 101. Cototient(x) = 102 only for x = 202 so a(102) = 1.
%t A063740 Table[Count[Range[n^2], k_ /; k - EulerPhi@ k == n], {n, 2, 105}] (* _Michael De Vlieger_, Mar 17 2017 *)
%o A063740 (PARI) first(n)=my(v=vector(n),t); forcomposite(k=4,n^2, t=k-eulerphi(k); if(t<=n, v[t]++)); v[2..n] \\ _Charles R Greathouse IV_, Mar 17 2017
%Y A063740 Cf. A000010, A051953, A063507.
%Y A063740 Cf. A063748 (greatest solution to x-phi(x)=n).
%Y A063740 Cf. A005278, A063741, A131825.
%K A063740 nonn
%O A063740 2,3
%A A063740 _Labos Elemer_, Aug 13 2001
%E A063740 Name edited by _Charles R Greathouse IV_, Mar 17 2017