A230164 - OEIS

%I #17 Jul 28 2024 17:02:42

%S 17296,24016,334144656,358585488,2955423888,311063879024

%N Numbers k such that k' = sigma(k), where k' is the arithmetic derivative of k.

%C a(7) > 10^12. - _Giovanni Resta_, Mar 11 2014

%e If k = 17296 then k' = sigma(k) = 35712. If k = 24016 then k' = sigma(k) = 49600.

%p with(numtheory); P:= proc(q) local a,n,p;

%p for n from 1 to q do a:=n*add(op(2,p)/op(1,p),p=ifactors(n)[2]);

%p if sigma(n)=a then print(n); fi; od; end: P(10^9);

%Y Cf. A003415, A229342, A230165, A342021.

%K nonn,more

%O 1,1

%A _Paolo P. Lava_, Oct 14 2013

%E a(3)-a(5) from _Giovanni Resta_, Oct 14 2013

%E a(6) from _Giovanni Resta_, Mar 11 2014