A086779 Numbers k such that k-th cyclotomic polynomial has exactly 7 nonzero terms.

7, 14, 15, 28, 30, 45, 49, 56, 60, 75, 90, 98, 112, 120, 135, 150, 180, 196, 224, 225, 240, 270, 300, 343, 360, 375, 392, 405, 448, 450, 480, 540, 600, 675, 686, 720, 750, 784, 810, 896, 900, 960, 1080, 1125, 1200, 1215, 1350, 1372, 1440, 1500, 1568, 1620

Offset: 1

Author

Yuval Dekel (dekelyuval(AT)hotmail.com), Aug 03 2003

Keywords

• nonn

Crossrefs

Cf. A086761.

Programs

Mathematica

Select[Range[2000], Count[CoefficientList[Cyclotomic[#, x], x], 0] == EulerPhi[#] - 6 &] (* T. D. Noe, Feb 13 2012 *)

PARI

isok(n) = {my(p = polcyclo(n)); #select(x->x, vector(1+poldegree(p), k, polcoeff(p, k-1))) == 7;} \\ Michel Marcus, Oct 26 2017

Formula

{n: A051664(n)=7}. - R. J. Mathar, Sep 15 2012

Extensions

Extended by T. D. Noe, Feb 13 2012