

A206075


Nonprimes in A206074 (a coding of irreducible polynomials).


6



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
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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 *)


PROG

(PARI) is(n)=n==1  (polisirreducible( Pol(binary(n)) ) && !isprime(n)) \\ Charles R Greathouse IV, May 14 2015


CROSSREFS

Cf. A206074.
Sequence in context: A349416 A157269 A186892 * A276448 A176275 A108166
Adjacent sequences: A206072 A206073 A206074 * A206076 A206077 A206078


KEYWORD

nonn


AUTHOR

Clark Kimberling, Feb 03 2012


STATUS

approved



