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

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

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.

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