OFFSET
1,1
COMMENTS
n is in the sequence if and only if A204455(n) is in the sequence. - Robert Israel, Apr 17 2019
LINKS
Robert Israel, Table of n, a(n) for n = 1..2000
M. Beiter, The midterm coefficient of the cyclotomic polynomial F_{pq}(x), Amer. Math. Monthly 71 (1964), 769-770.
G. Dresden, On the Middle Coefficient of a Cyclotomic Polynomial, Amer. Math. Monthly 111 (2004), 531-533.
EXAMPLE
385 is the first item in the list because Phi(385,x) is the first cyclotomic polynomial with middle coefficient different from -1,0,1 (the middle term is -3x^120)
MAPLE
filter:= proc(n) local p, d;
p:= numtheory:-cyclotomic(n, x);
d:= degree(p, x);
abs(coeff(p, x, d/2))>1
end proc:
select(filter, [$3..5000]); # Robert Israel, Apr 17 2019
MATHEMATICA
Select[Range[3, 4000],
Abs[Coefficient[Cyclotomic[#, x], x, EulerPhi[#]/2]] > 1 &]
PROG
(PARI) isok(n) = (n > 2) && (abs(polcoeff(polcyclo(n), eulerphi(n)/2)) > 1); \\ Michel Marcus, Aug 02 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Greg Dresden, Jul 25 2018
STATUS
approved