

A086779


Numbers k such that kth cyclotomic polynomial has exactly 7 nonzero terms.


1



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
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OFFSET

1,1


LINKS

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


FORMULA

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


EXAMPLE

7 is a member because the 7th cyclotomic polynomial is P(x) = x^6 + x^5 + x^4 + x^3 + x^2 + x + 1 that has 7 coefficients.  Paolo P. Lava, Oct 26 2017


MAPLE

with(numtheory): P:=proc(n) local x;
if nops([coeffs(cyclotomic(n, x))])=7 then n; fi;
end: seq(P(j), j=1..1620); # Paolo P. Lava, Oct 26 2017


MATHEMATICA

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


PROG

(PARI) isok(n) = {my(p = polcyclo(n)); #select(x>x, vector(1+poldegree(p), k, polcoeff(p, k1))) == 7; } \\ Michel Marcus, Oct 26 2017


CROSSREFS

Cf. A086761.
Sequence in context: A062056 A173024 A115770 * A269173 A167197 A336797
Adjacent sequences: A086776 A086777 A086778 * A086780 A086781 A086782


KEYWORD

nonn


AUTHOR

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


EXTENSIONS

Extended by T. D. Noe, Feb 13 2012


STATUS

approved



