A278570 - OEIS

%I #18 Oct 19 2017 10:46:18

%S 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,

%T 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,

%U 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

%N 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).

%D _Don Reble_, Posting to Sequence Fans Mailing List, Nov 26 2016

%H Alois P. Heinz, <a href="/A278570/b278570.txt">Table of n, a(n) for n = 1..20000</a>

%p with(numtheory):

%p b:= proc(n) option remember; local k;

%p       for k from 2+`if`(n=1, 1, b(n-1)) by 2 while

%p       bigomega(k)<>3 or nops(factorset(k))<>3 do od; k

%p     end:

%p a:= n-> max(map(abs, [coeffs(cyclotomic(b(n), x))])):

%p seq(a(n), n=1..120);  # _Alois P. Heinz_, Nov 27 2016

%t b[n_] := b[n] = (For[k = 2 + If[n == 1, 1, b[n-1]], PrimeOmega[k] != 3 || PrimeNu[k] != 3, k += 2]; k);

%t a[n_] :=  Max @ Abs @ CoefficientList[Cyclotomic[b[n], x], x];

%t Array[a, 120] (* _Jean-François Alcover_, Mar 28 2017, after _Alois P. Heinz_ *)

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

%K nonn

%O 1,1

%A _N. J. A. Sloane_, Nov 27 2016