login
This site is supported by donations to The OEIS Foundation.

 

Logo

Invitation: celebrating 50 years of OEIS, 250000 sequences, and Sloane's 75th, there will be a conference at DIMACS, Rutgers, Oct 9-10 2014.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A140803 Numbers of the form (2^(pq)-1) /((2^p-1)*(2^q-1)), where p>q are primes. 1
3, 11, 43, 151, 683, 2359, 2731, 43691, 174763, 599479, 2796203, 8727391, 9588151, 178956971, 715827883, 2454285751 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The sequence contains, in particular, A126614 (q=2) and A143012 (q=3).

If pq-1 is squarefree then the terms of the sequence are either primes or overpseudoprimes to base 2 (see A141232). In particular, they are strong pseudoprimes to base 2 (A001262).

LINKS

Table of n, a(n) for n=1..16.

V. Shevelev, Process of "primoverization" of numbers of the form a^n-1, arXiv:0807.2332

S. Wagstaff, Factorizations of 2^n-1

EXAMPLE

Entry 3 from (q=2,p=3), entry 11 from (q=2,p=5), entry 43 from (q=2,p=7), entry 151 from (q=3,p=5), entry 683 from (q=2,p=11).

CROSSREFS

Cf. A001262, A141232, A126614, A143012.

Sequence in context: A118166 A106876 A034477 * A084643 A007583 A026671

Adjacent sequences:  A140800 A140801 A140802 * A140804 A140805 A140806

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Jul 15 2008, Jul 22 2008; corrected Sep 07 2008

STATUS

approved

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

Content is available under The OEIS End-User License Agreement .

Last modified September 2 10:51 EDT 2014. Contains 246353 sequences.