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A002475
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Numbers k such that x^k + x + 1 is irreducible over GF(2).
(Formerly M0544 N0194)
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23
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0, 2, 3, 4, 6, 7, 9, 15, 22, 28, 30, 46, 60, 63, 127, 153, 172, 303, 471, 532, 865, 900, 1366, 2380, 3310, 4495, 6321, 7447, 10198, 11425, 21846, 24369, 27286, 28713, 32767, 34353, 46383, 53484, 62481, 83406, 87382, 103468, 198958, 248833
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OFFSET
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1,2
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COMMENTS
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k=1 is excluded since the polynomial "1" is not normally regarded as irreducible.
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REFERENCES
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N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 975.
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LINKS
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MAPLE
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select(n -> Irreduc(x^n+x+1) mod 2, [0, $2..10000]); # Robert Israel, Aug 09 2015
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MATHEMATICA
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Do[ If[ ToString[ Factor[ x^n + x + 1, Modulus -> 2 ] ] == ToString[ x^n + x + 1 ], Print [ n ] ], {n, 0, 28713} ]
Select[Range[1000], IrreduciblePolynomialQ[x^# + x + 1, Modulus -> 2] &] (* Robert Price, Sep 19 2018 *)
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PROG
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(Magma) P<x> := PolynomialRing(GaloisField(2)); for n := 2 to 100000 do if IsIrreducible(x^n+x+1) then print(n); end if; endfor;
(Sage)
P.<x> = GF(2)[]
for n in range(90):
if (x^n+x+1).is_irreducible():
(PARI)
for (n=1, 10^6, if ( polisirreducible(Mod(1, 2)*(x^n+x+1)), print1(n, ", ") ) );
(PARI) is(n)=if(n>3&&[1, 0, 1, 1, 0, 1, 0, 0][n%8+1], return(0)); polisirreducible(Mod('x^n+'x+1, 2)) \\ Charles R Greathouse IV, Jun 04 2015
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CROSSREFS
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KEYWORD
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nonn,hard,more,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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