A290543 - OEIS

%I #15 Sep 08 2022 08:46:19

%S 28,65,66,85,91,105,117,121,124,133,145,153,154,165,185,186,190,205,

%T 217,221,231,244,246,247,259,273,276,280,286,292,301,305,310,325,341,

%U 343,344,357,364,366,369,370,377,385,396,418,425,427,429,430,435,451

%N Composite numbers n such that A290542(n) >= 2.

%C Is a(n) ~ n * log n as n -> infinity?

%t Select[Flatten@ Position[#, k_ /; k >= 2], CompositeQ] &@ Table[SelectFirst[Range[2, Sqrt@ n], PowerMod[#, n , n] == Mod[#, n] &], {n, 451}] (* _Michael De Vlieger_, Aug 09 2017 *)

%o (Magma) lst:=[]; for n in [4..451] do if not IsPrime(n) then r:=Floor(Sqrt(n)); for k in [2..r] do if Modexp(k, n, n) eq k then Append(~lst, n); break; end if; end for; end if; end for; lst;

%Y Cf. A001567, A006935, A122780, A122781, A122782, A122783, A122784, A122785, A122786, A290542.

%K nonn

%O 1,1

%A _Arkadiusz Wesolowski_, Aug 05 2017