A278570 a(n) = maximum absolute value of coefficients in the cyclotomic polynomial C(N,x), where N = n-th number which a product of three distinct odd primes = A046389(n).

2, 2, 2, 1, 2, 2, 2, 2, 2, 3, 1, 2, 1, 2, 1, 1, 2, 2, 3, 2, 2, 2, 2, 1, 1, 3, 2, 2, 1, 2, 2, 2, 2, 1, 1, 2, 1, 1, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 2, 1, 2, 1, 2, 3, 2, 2, 2, 1, 2, 3, 1, 1, 1, 2, 2, 2, 1, 2, 3, 1, 2, 3, 2, 2, 1, 2, 2, 2, 1, 2, 1, 2, 2, 2, 2, 1, 2, 2, 2, 2, 3, 1, 2, 2, 2, 1, 3, 2

Offset: 1

Author

N. J. A. Sloane, Nov 27 2016

Keywords

• nonn

References

• Don Reble, Posting to Sequence Fans Mailing List, Nov 26 2016

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..20000

Crossrefs

Cf. A046389. See A278567 for a closely related sequence.

Programs

Maple

with(numtheory):
b:= proc(n) option remember; local k;
      for k from 2+`if`(n=1, 1, b(n-1)) by 2 while
      bigomega(k)<>3 or nops(factorset(k))<>3 do od; k
    end:
a:= n-> max(map(abs, [coeffs(cyclotomic(b(n), x))])):
seq(a(n), n=1..120);  # Alois P. Heinz, Nov 27 2016

Mathematica

b[n_] := b[n] = (For[k = 2 + If[n == 1, 1, b[n-1]], PrimeOmega[k] != 3 || PrimeNu[k] != 3, k += 2]; k);
a[n_] :=  Max @ Abs @ CoefficientList[Cyclotomic[b[n], x], x];
Array[a, 120] (* Jean-François Alcover, Mar 28 2017, after Alois P. Heinz *)