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A207669 Numbers that match polynomials irreducible (mod 3), with coefficients in {0,1,2}.

%I A207669 #15 Aug 19 2021 10:56:25
%S A207669 3,4,5,6,7,8,10,14,17,20,22,25,34,35,38,41,43,46,49,53,58,59,65,67,71,
%T A207669 73,77,79,86,89,92,94,97,101,110,115,118,121,125,134,137,139,145,149,
%U A207669 151,158,166,169,172,181,185,188,190,197,205,209,212,214,217
%N A207669 Numbers that match polynomials irreducible (mod 3), with coefficients in {0,1,2}.
%C A207669 For such polynomials irreducible over the field of rational numbers, see A207966, which also describes the enumeration of all the nonzero polynomials whose coefficients are all in {0,1,2}.
%e A207669 Polynomials having coefficients in {0,1,2} are
%e A207669 enumerated by the positive integers as follows:
%e A207669 n ... p[n,x] .. irreducible (mod 3)
%e A207669 1 ... 1 ....... no
%e A207669 2 ... 2 ....... no
%e A207669 3 ... x ....... yes
%e A207669 4 ... x+1 ..... yes
%e A207669 5 ... x+2 ..... yes
%e A207669 6 ... 2x ...... yes
%e A207669 7 ... 2x+1 .... yes
%e A207669 8 ... 2x+2 .... yes
%e A207669 9 ... x^2 ..... no
%e A207669 10 .. x^2+1 ... yes
%e A207669 11 .. x^2+2 ... no
%e A207669 The least n for which p(n,x) is irreducible over the
%e A207669 rationals but not modulo 3 is 13; the factorization of
%e A207669 p(13,x) is (x+1)(x+2) (mod 3).
%t A207669 t = Table[IntegerDigits[n, 3], {n, 1, 1000}];
%t A207669 b[n_] := Reverse[Table[x^k, {k, 0, n}]]
%t A207669 p[n_, x_] := t[[n]].b[-1 + Length[t[[n]]]]
%t A207669 Table[p[n, x], {n, 1, 15}]
%t A207669 u = {}; Do[n++;
%t A207669 If[IrreduciblePolynomialQ[p[n, x], Modulus -> 3],
%t A207669   AppendTo[u, n]], {n, 1, 400}]
%t A207669 u                           (* A207669 *)
%t A207669 Complement[Range[200], %]   (* A207670 *)
%t A207669 b[n_] := FromDigits[IntegerDigits[u, 3][[n]]]
%t A207669 Table[b[n], {n, 1, 50}]     (* A207671 *)
%Y A207669 Cf. A207670 (complement), A207671 (ternary).
%K A207669 nonn
%O A207669 1,1
%A A207669 _Clark Kimberling_, Feb 26 2012