%I #7 Apr 14 2017 03:00:13

%S 29,11,41,71,17,23,53,23,131,41,307,509,61,181,37,191,41,229,239,89,

%T 47,797,73,571,499,157,59,643,73,71,739,373,71,607,359,419,83,431,433,

%U 89,443,941,83,1481,109,251,1553,1061,101,1721,101,401,599,251,131

%N Least prime r > q such that the third-order cyclotomic polynomial Phi(pqr,x) is flat with p,q,r distinct odd primes, ordered by pq.

%C A flat polynomial is defined to be a polynomial whose coefficients are -1, 0, or 1. Sequence A046388 gives the product pq. As proved by Kaplan, given odd primes p < q, it is always possible to find a prime r > q such that Phi(pqr,x) is flat.

%H Nathan Kaplan, <a href="https://doi.org/10.1016/j.jnt.2007.01.008">Flat cyclotomic polynomials of order three</a>, J. Number Theory 127 (2007), 118-126.

%e a(1)=29 because 15*29 is the least multiple of 15 that produces a flat cyclotomic polynomial.

%Y Cf. A046388, A117223.

%K nonn

%O 1,1

%A _T. D. Noe_, May 15 2009