OFFSET
1,2
COMMENTS
The cyclotomic polynomial Phi[pqr] (p,q,r primes) can only have coefficients with absolute value > 1 if p,q,r are distinct odd primes. This sequence also counts the trivial cases where (1): p=2, or (2): p=q, or (3): q=r. The number of these cases is A008486(n-1). Sequence A159909 counts only the nontrivial cases.
LINKS
Robin Visser, Table of n, a(n) for n = 1..130
Phil Carmody, "Cyclotomic polynomial puzzles", in: "primenumbers" group, May 9, 2009.
Phil Carmody, David Broadhurst, Maximilian Hasler, Makoto Kamada, Cyclotomic polynomial puzzles, digest of 43 messages in primenumbers Yahoo group, May 9, 2009 - May 23, 2013.
Eric Weisstein's World of Mathematics, Cyclotomic Polynomial.
PROG
(PARI) A159908(n) = sum( i=1, n, my(pq=prime(n)*prime(i)); sum( j=1, i, vecmax(abs(Vec(polcyclo(prime(j)*pq))))==1 ))
CROSSREFS
KEYWORD
hard,nonn
AUTHOR
M. F. Hasler, May 09 2009
EXTENSIONS
More terms from Robin Visser, Aug 09 2023
STATUS
approved