A206075 - OEIS

A206075

Nonprimes in A206074 (a coding of irreducible polynomials).

1, 25, 55, 69, 77, 81, 87, 91, 115, 117, 121, 143, 145, 169, 171, 185, 203, 205, 209, 213, 247, 253, 261, 265, 275, 285, 289, 295, 299, 301, 305, 319, 321, 323, 327, 329, 333, 339, 351, 355, 357, 361, 369, 375, 377, 391, 395, 405, 407, 415, 425, 437

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

EXAMPLE

Under the coding of irreducible polynomials over {0,1} which is given at A206074, the polynomials matching the first five terms of A206075 are indicated here:

1 .... 1

25 ... x^4 + x^3 + 1

55 ... x^5 + x^4 + x^2 + x + 1

69 ... x^6 + x^2 + 1

77 ... x^6 + x^3 + x^2 + 1

MATHEMATICA

t = Table[IntegerDigits[n, 2], {n, 1, 1500}];

b[n_] := Reverse[Table[x^k, {k, 0, n}]]

p[n_, x_] := t[[n]].b[-1 + Length[t[[n]]]]

u = {1}; Do[n++; If[IrreduciblePolynomialQ[p[n, x]], AppendTo[u, n]], {n, 1000}]

nonprimes = Complement[Range[800], Table[Prime[n], {n, 1, 800}]];

Intersection[u, nonprimes] (* A206075 *)