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!)
A086761 Numbers n such that n-th cyclotomic polynomial has exactly 5 nonzero terms. 2
5, 10, 20, 25, 40, 50, 80, 100, 125, 160, 200, 250, 320, 400, 500, 625, 640, 800, 1000, 1250, 1280, 1600, 2000, 2500, 2560, 3125, 3200, 4000, 5000, 5120, 6250, 6400, 8000, 10000, 10240, 12500, 12800, 15625, 16000, 20000, 20480, 25000, 25600, 31250, 32000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A206787(a(n)) = 6. [Reinhard Zumkeller, Feb 12 2012]

All terms have the form 2^a 5^b with a >= 0 and b > 0. - T. D. Noe, Feb 13 2012

LINKS

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

MATHEMATICA

Select[Range[1000], Count[CoefficientList[Cyclotomic[#, x], x], 0] == EulerPhi[#] - 4 &] (* T. D. Noe, Feb 13 2012 *)

CROSSREFS

Cf. A051664, A065119.

Sequence in context: A245387 A115799 A072703 * A045191 A065958 A065969

Adjacent sequences:  A086758 A086759 A086760 * A086762 A086763 A086764

KEYWORD

nonn

AUTHOR

Yuval Dekel (dekelyuval(AT)hotmail.com), Aug 02 2003

EXTENSIONS

More terms from T. D. Noe, Feb 13 2012

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 October 1 12:17 EDT 2014. Contains 247510 sequences.