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

2, 777, 98433, 214388517, 152739317354

Offset: 1

Author

Paolo P. Lava, Jun 18 2013

Keywords

• nonn
• more

Comments

a(6) > 10^13. - Giovanni Resta, Mar 13 2014

a(6) > 5*10^13. - Hiroaki Yamanouchi, Aug 27 2015

Examples

			2' = 3' = 1
777' = 778' = 391
98433' = 98434' = 65631
214388517' = 214388518' = 107194261
		

Crossrefs

Cf. A003415

Programs

Maple

with(numtheory); ListA226779:=proc(q) local a,b,n,p; a:=0;
for n from 2 to q do b:=n*add(op(2,p)/op(1,p),p=ifactors(n)[2]);
  if a=b then print(n-1); fi; a:=b; od; end: ListA226779(10^12);

Extensions

a(5) from Giovanni Resta, Jun 18 2013