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 A086779 Numbers k such that k-th 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS 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, 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, k-1))) == 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

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Last modified April 23 10:07 EDT 2021. Contains 343204 sequences. (Running on oeis4.)