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 A098202 #15 Nov 19 2024 03:00:50
%S A098202 3,5,8,12,18,20,31,32,41,43,61,65,80,77,95,125,131,125,157,173,140,
%T A098202 192,195,221,213,212,261,269,277,300,296,321,336,329,358,367,379,405,
%U A098202 428,439,438,464,477,493,506,454,491,542,564,588,543,600,639,660
%N A098202 a(n) is the length of the iteration trajectory when the cototient function (A051953) is applied to the n-th primorial number (A002110(n)).
%F A098202 a(n) = A053475(A002110(n)). - _Robert G. Wilson v_, Sep 22 2004
%e A098202 For n = 3: list = {30,22,12,8,4,2,1,0}, a(4) = 8.
%t A098202 g[x_] := x - EulerPhi[x]; f[x_] := Length[ FixedPointList[g, x]] - 1; q[x_] := Product[ Prime[j], {j, x}]; Table[ f[ q[n]], {n, 33}]
%t A098202 a[n_] := Length@ NestWhileList[(# - EulerPhi[#])&, Times @@ Prime[Range[n]], # > 0 &]; Array[a, 30] (* _Amiram Eldar_, Nov 19 2024 *)
%o A098202 (PARI) a(n) = {my(p = prod(i=1, n, prime(i)), c = 1); while(p > 0, c++; p -= eulerphi(p)); c;} \\ _Amiram Eldar_, Nov 19 2024
%Y A098202 Cf. A002110, A051953, A053475, A098115.
%K A098202 nonn,more
%O A098202 1,1
%A A098202 _Labos Elemer_, Sep 22 2004
%E A098202 More terms from _Robert G. Wilson v_, Sep 22 2004
%E A098202 a(37)-a(54) from _Amiram Eldar_, Nov 19 2024