cp's OEIS Frontend

A226779 Numbers n such that n'=(n+1)', where n' is the arithmetic derivative of n.

%I A226779 #17 Aug 27 2015 08:17:12
%S A226779 2,777,98433,214388517,152739317354
%N A226779 Numbers n such that n'=(n+1)', where n' is the arithmetic derivative of n.
%C A226779 a(6) > 10^13. - _Giovanni Resta_, Mar 13 2014
%C A226779 a(6) > 5*10^13. - _Hiroaki Yamanouchi_, Aug 27 2015
%e A226779 2' = 3' = 1
%e A226779 777' = 778' = 391
%e A226779 98433' = 98434' = 65631
%e A226779 214388517' = 214388518' = 107194261
%p A226779 with(numtheory); ListA226779:=proc(q) local a,b,n,p; a:=0;
%p A226779 for n from 2 to q do b:=n*add(op(2,p)/op(1,p),p=ifactors(n)[2]);
%p A226779   if a=b then print(n-1); fi; a:=b; od; end: ListA226779(10^12);
%Y A226779 Cf. A003415
%K A226779 nonn,more
%O A226779 1,1
%A A226779 _Paolo P. Lava_, Jun 18 2013
%E A226779 a(5) from _Giovanni Resta_, Jun 18 2013