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 A349676 #13 Nov 27 2021 12:00:17 %S A349676 2,3,5,9,21,65,225,1365,14625,223125,5630625,376228125,38759765625, %T A349676 3471767578125,934835712890625,497199051298828125, %U A349676 613613372156103515625,2538878964828409423828125,25280374785655551910400390625,243473923053903449878692626953125,9202204429788304689688510894775390625 %N A349676 Iterated Pillai's arithmetical function: a(1) = 2, for n >= 2, a(n) = A018804(a(n-1)). %F A349676 a(1) = 2, a(n) = A018804(a(n-1)) for n >= 2. %e A349676 a(5) = f(f(f(f(a(1))))) = 21. Here f represents A018804. %t A349676 f[p_, e_] := (e*(p - 1)/p + 1) * p^e; pil[n_] := Times @@ f @@@ FactorInteger[n]; NestList[pil, 2, 20] (* _Amiram Eldar_, Nov 24 2021 *) %o A349676 (PARI) f(n) = sumdiv(n, d, n*eulerphi(d)/d); \\ A018804 %o A349676 lista(nn) = my(a = 2); for (n=1, nn, print1(a, ", "); a = f(a);); \\ _Michel Marcus_, Nov 24 2021 %Y A349676 Cf. A018804. %K A349676 nonn %O A349676 1,1 %A A349676 _Ctibor O. Zizka_, Nov 24 2021 %E A349676 More terms from _Michel Marcus_, Nov 24 2021