OFFSET
1,1
COMMENTS
Sequence appears to consist of 3^i, i > 0; and 2^i*5^j, i, j > 0. Are there any other terms? - David Wasserman, Feb 01 2005
EXAMPLE
9 is a member because the 9th cyclotomic polynomial is P(x) = x^6+x^3+1.
MATHEMATICA
Select[Range@ 5000, Count[CoefficientList[Cyclotomic[#, x], x], _?(# > 0 &)] == 3 &] (* Michael De Vlieger, Oct 26 2017 *)
PROG
(PARI) n = 0; while (1, n++; p = polcyclo(n, x); d = poldegree(p); c = 0; i = 0; while (c < 4 && i <= d, if (polcoeff(p, i) > 0, c++); i++); if (c == 3, print(n))); \\ David Wasserman, Feb 01 2005
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Yuval Dekel (dekelyuval(AT)hotmail.com), Aug 14 2003
EXTENSIONS
More terms from David Wasserman, Feb 01 2005
STATUS
approved