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

 

Logo

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A039772 phi(a(n)) and (a(n)-1) have a common factor, are distinct and a(n) is even. 3
28, 52, 66, 70, 76, 112, 124, 130, 148, 154, 172, 176, 186, 190, 196, 208, 232, 238, 244, 246, 268, 276, 280, 286, 292, 304, 310, 316, 322, 344, 364, 366, 370, 388, 396, 406, 412, 418, 426, 430, 436, 442, 448, 490, 496, 506, 508, 520, 532, 556, 568, 574 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also a(n) is the union of all possible even Fermat pseudoprimes q to some prime base p>q such that q does not divide p-1. Note that all even nonprime divisors of p-1 are the Fermat pseudoprimes to prime base p. E.g. q = {4,6,12,18,28,36} is a set of even Fermat pseudoprimes to prime base p = 37, but only number q = 28 from this set does not divide p-1 = 36. - Alexander Adamchuk, Jun 16 2007

LINKS

Table of n, a(n) for n=1..52.

Romeo Meštrović, Generalizations of Carmichael numbers I, arXiv:1305.1867v1 [math.NT], May 4, 2013.

Eric Weisstein, Link to a section of The World of Mathematics. Fermat Pseudoprime.

EXAMPLE

phi(28)=12, gcd(12,27)=3.

CROSSREFS

Cf. A000010.

Sequence in context: A046419 A063770 A161923 * A181792 A181793 A224545

Adjacent sequences:  A039769 A039770 A039771 * A039773 A039774 A039775

KEYWORD

nonn,easy

AUTHOR

Olivier Gérard

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 December 21 17:16 EST 2014. Contains 252324 sequences.