A160686 Numbers n such that n/A000005(A000045(n)) is an integer.

1, 2, 4, 8, 16, 32, 64

Offset: 1

Author

Ctibor O. Zizka, May 23 2009

Keywords

• nonn
• hard
• more

Comments

The first power of 2 not in this sequence is 2^7 = 128, because 128/A000005(A000045(128)) = 1/2, which is not an integer. - Nathaniel Johnston, May 08 2011

Next term, if it exists, is greater than 3000. Conjecture: the sequence is finite and complete. - Max Alekseyev, May 21 2011

Crossrefs

Cf. A000005, A000045, A000079, A160683.

Programs

Maple

with(combinat):with(numtheory): A160686 := proc(n) option remember: local k: if(n=1)then return 1:fi: for k from procname(n-1)+1 do if(k mod tau(fibonacci(k))=0)then return k:fi: od: end: seq(A160686(n),n=1..7); # Nathaniel Johnston, May 08 2011

Formula

{n: A063375(n) | n}. - R. J. Mathar, May 25 2009

Extensions

Inverted division in the definition - R. J. Mathar, May 25 2009

Erroneous term a(5) = 12 removed by Nathaniel Johnston, May 08 2011