A333264 - OEIS

%I #4 Mar 13 2020 20:47:14

%S 1,2,3,4,5,8,15,17,69,121,137,467,985,1949,4049,8117,14641,36383,

%T 62501,125003,250007,958081,1817513,3325981,8062091,21233813,42467627,

%U 125828819,343955189

%N Least number k that reaches 1 after n iterations of A206369.

%C Least number k such that A330786(k) = n.

%e a(5) = 8 since 8 is the least number that reaches 1 after 5 iterations of A206369: 8 -> 5 -> 4 -> 3 -> 2 -> 1.

%t f[p_, e_] := Sum[(-1)^(e-k)*p^k, {k, 0, e}]; s[1] = 1; s[n_] := Times @@ (f @@@ FactorInteger[n]); numiter[n_] := Length @ FixedPointList[s, n] - 2; n = 0; seq={}; Do[If[numiter[k] == n, AppendTo[seq, k]; n++], {k, 1, 1000}]; seq

%Y Cf. A206369, A330786.

%K nonn,more

%O 0,2

%A _Amiram Eldar_, Mar 13 2020