%N The least k for which A335884(k) = n.
%C Because A335884 is fully additive and a(1) = 3, we have a(n) <= 3^n and in particular, a(n+1) <= 3*a(n), n > 0 and more generally a(n + m) <= a(n) * a(m) where m, n >= 0. (See also comments in A334099.)
%C a(16) = 208849 = 457^2 = a(8)*a(8) is the first composite term.
%F For all n >= 0, A335884(a(n)) = n.
%Y Cf. A335884.
%A _Antti Karttunen_, Jun 29 2020
%E a(21)-a(23) from _Jinyuan Wang_, Jul 08 2020