A347931 - OEIS

%I #22 Oct 16 2021 19:26:54

%S 1,4,8,16,24,27,48,54,64,108,128,162,168,256,320,324,432,512,704,729,

%T 864,1024,1134,1728,2048,2160,2187,2192,2916,3125,3456,4096,4752,5120,

%U 5832,6250,6912,11664,12500,13824,14580,14796,16384,18750,19683,23328,27648

%N Nonprime numbers that divide their second arithmetic derivative.

%H Alois P. Heinz, <a href="/A347931/b347931.txt">Table of n, a(n) for n = 1..250</a>

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Arithmetic_derivative">Arithmetic derivative</a>

%F { A348284 } minus { A000040 }.

%F { A018252 } intersect { A348284 }.

%p d:= n-> n*add(i[2]/i[1], i=ifactors(n)[2]):

%p q:= n-> not isprime(n) and irem(d(d(n)), n)=0:

%p select(q, [$1..30000])[];  # _Alois P. Heinz_, Oct 15 2021

%Y Cf. A000040, A003415, A018252, A068346, A348284.

%K nonn

%O 1,2

%A _Alois P. Heinz_, Oct 15 2021