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%I #14 Oct 13 2021 16:41:53
%S 2,3,4,5,7,11,13,17,19,23,27,29,31,37,41,43,47,53,59,61,67,71,73,79,
%T 83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,
%U 179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293
%N Numbers k such that k' | k.
%C Here, m' denotes the arithmetic derivative of m (A003415).
%C Not the same as A211781 since this sequence does not contain 225, 252, etc.
%C All prime numbers p are in the sequence since p' = 1 | p.
%e 127 is in the sequence since 127' = 1 | 127.
%p q:= n-> is(irem(n, n*add(i[2]/i[1], i=ifactors(n)[2]))=0):
%p select(q, [$2..300])[]; # _Alois P. Heinz_, Oct 11 2021
%o (PARI) ad(n) = vecsum([n/f[1]*f[2]|f<-factor(n+!n)~]); \\ A003415
%o isok(k) = (k>1) && !(k % ad(k)); \\ _Michel Marcus_, Oct 10 2021
%Y Cf. A003415, A211781.
%K nonn
%O 1,1
%A _Wesley Ivan Hurt_, Oct 09 2021
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