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

2, 777, 98433, 214388517, 152739317354

Offset

1,1

Comments

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

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

Links

Table of n, a(n) for n=1..5.

Example

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

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);

Crossrefs

Cf. A003415

Sequence in context: A167448 A320481 A078169 * A375844 A243409 A281195

Adjacent sequences: A226776 A226777 A226778 * A226780 A226781 A226782

Keyword

nonn,more

Author

Paolo P. Lava, Jun 18 2013

Extensions

a(5) from Giovanni Resta, Jun 18 2013

Status

approved