login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A072611 Numbers n such that phi(n) divides sigma(n+1)-sigma(n). 0
1, 2, 6, 14, 30, 40, 70, 140, 170, 174, 206, 215, 238, 390, 459, 518, 923, 957, 1334, 1364, 1540, 1634, 2685, 2974, 4364, 5180, 5934, 6048, 6467, 6510, 6623, 8028, 8094, 8260, 8814, 12136, 12954, 14099, 14841, 15416, 16472, 17094, 17835, 17927, 18873 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..45.

FORMULA

Conjecture : lim n -> infinity Log(a(n))/Log(n) exists = 2, 6.......

MATHEMATICA

Select[Range[20000], Divisible[DivisorSigma[1, #+1]-DivisorSigma[1, #], EulerPhi[#]]&] (* Harvey P. Dale, Sep 15 2011 *)

CROSSREFS

Sequence in context: A063452 A009299 A330766 * A284023 A192966 A339668

Adjacent sequences:  A072608 A072609 A072610 * A072612 A072613 A072614

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Aug 07 2002

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 19 18:36 EDT 2021. Contains 347564 sequences. (Running on oeis4.)