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A086761 Numbers k such that k-th cyclotomic polynomial has exactly 5 nonzero terms. 3
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

If the above holds for all terms then this sequence is 5 * A003592. - David A. Corneth, Jul 04 2018

LINKS

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

MAPLE

with(numtheory): P:=proc(n) local x;

if nops([coeffs(cyclotomic(n, x))])=5 then n; fi;

end: seq(P(j), j=1..32000); # Paolo P. Lava, Jul 04 2018

MATHEMATICA

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

PROG

(PARI) is(n) = v = Vec(polcyclo(n)); sum(i=1, #v, v[i]!=0) == 5 \\ David A. Corneth, Jul 04 2018

CROSSREFS

Cf. A003592, 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

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Last modified October 18 04:57 EDT 2019. Contains 328145 sequences. (Running on oeis4.)