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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
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
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
KEYWORD
nonn
AUTHOR
Yuval Dekel (dekelyuval(AT)hotmail.com), Aug 02 2003
EXTENSIONS
More terms from T. D. Noe, Feb 13 2012
STATUS
approved