A208135 -id:A208135 - cp's OEIS frontend

A208136 Subsequence of A208135 with numbers that match duplicate factors deleted.

9, 33, 35, 39, 49, 57, 65, 129, 133, 135, 147, 159, 161, 183, 201, 215, 225, 235, 237, 249, 259, 267, 287, 291, 303, 371, 385, 393, 413, 417, 423, 427, 459, 489, 497, 519, 525, 527, 537, 543, 573, 579, 591, 605, 609, 615, 633, 651

Offset: 1

Clark Kimberling, Feb 23 2012

nonn

The polynomials having coefficients in {0,1} are enumerated at A206073. They include the following:
  p(1,x) = 1
  p(2,x) = x
  p(3,x) = x + 1
  p(9,x) = x^3 + 1 = (x + 1)*(x^2 - x + 1)
  p(18,x) = x*(x + 1)*(x^2 - x + 1)
  p(33,x) = (x + 1)*(x^4 - x^3 + x^2 - x + 1).
A208135 gives those n for which p(n,x) has a factor containing a negative coefficient; A208136 is a subsequence of A208135 in which, for each p(n,x), there is a factor containing a negative coefficient, and that factor has not already occurred for some p(k,x) with k

			The first few polynomial factors having a negative coefficient are as follows:
  x^2 - x + 1 divides p(n,x) for n=9,18,21,27,36,42,...
  x^4 - x^3 + x^2 - x + 1 divides p(n,x) for n=33,66,...
  x^3 - x^2 + 1 divides p(n,x) for n=35,70,...
  x^4 - x^3 + x^2 + 1 divides p(n,x) for n=39,...
  x^3 - x + 1 divides p(n,x) for n=49,...
  x^4 + x^2 - x + 1 divides p(n,x) for n=57,...
In A208136, the duplicates (such as 18, 21, 27, 36, 42, ...) are omitted.

Cf. A208135, A206073, A206284.

Remove["Global`*"];
t = Table[IntegerDigits[n, 2], {n, 1, 3000}];
b[n_] := Reverse[Table[x^k, {k, 0, n}]];
p[n_, x_] := p[n, x] = t[[n]].b[-1 + Length[t[[n]]]];
TableForm[Table[{n, p[n, x], Factor[p[n, x]]}, {n, 1, 900}]];
ans = DeleteCases[Table[{z, Cases[Sign[
       Table[CoefficientList[#[[n]], x], {n, 1, Length[#]}] &[Factor[p[z, x]]]], {_, -1, _}]}, {z, 1, 700}], {_, {}}];
n = 1; While[Length[ans] >= n,
ans = Delete[ans, Map[Take[{#[[1]]}] &, Rest[Position[ans, Flatten[ans[[n]][[2]]]]]]]; n++];
Map[#[[1]] &, ans]
(* Peter J. C. Moses, Feb 22 2012 *)

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A208136 Subsequence of A208135 with numbers that match duplicate factors deleted.

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