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 A347931 #22 Oct 16 2021 19:26:54
%S A347931 1,4,8,16,24,27,48,54,64,108,128,162,168,256,320,324,432,512,704,729,
%T A347931 864,1024,1134,1728,2048,2160,2187,2192,2916,3125,3456,4096,4752,5120,
%U A347931 5832,6250,6912,11664,12500,13824,14580,14796,16384,18750,19683,23328,27648
%N A347931 Nonprime numbers that divide their second arithmetic derivative.
%H A347931 Alois P. Heinz, <a href="/A347931/b347931.txt">Table of n, a(n) for n = 1..250</a>
%H A347931 Wikipedia, <a href="http://en.wikipedia.org/wiki/Arithmetic_derivative">Arithmetic derivative</a>
%F A347931 { A348284 } minus { A000040 }.
%F A347931 { A018252 } intersect { A348284 }.
%p A347931 d:= n-> n*add(i[2]/i[1], i=ifactors(n)[2]):
%p A347931 q:= n-> not isprime(n) and irem(d(d(n)), n)=0:
%p A347931 select(q, [$1..30000])[]; # _Alois P. Heinz_, Oct 15 2021
%Y A347931 Cf. A000040, A003415, A018252, A068346, A348284.
%K A347931 nonn
%O A347931 1,2
%A A347931 _Alois P. Heinz_, Oct 15 2021