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A091209
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Primes whose binary representation encodes a polynomial reducible over GF(2).
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25
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5, 17, 23, 29, 43, 53, 71, 79, 83, 89, 101, 107, 113, 127, 139, 149, 151, 163, 173, 179, 181, 197, 199, 223, 227, 233, 251, 257, 263, 269, 271, 277, 281, 293, 307, 311, 317, 331, 337, 347, 349, 353, 359, 367, 373, 383, 389, 401, 409, 421, 431, 439, 443, 449, 457, 461, 467, 479, 491, 503, 509, 521, 523
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OFFSET
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1,1
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COMMENTS
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"Encoded in binary representation" means that a polynomial a(n)*X^n+...+a(0)*X^0 over GF(2) is represented by the binary number a(n)*2^n+...+a(0)*2^0 in Z (where each coefficient a(k) = 0 or 1).
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LINKS
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FORMULA
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Other identities. For all n >= 1:
A235043(a(n)) = n. [A235043 works as a left inverse of this sequence.]
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MAPLE
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Primes:= select(isprime, [2, seq(2*i+1, i=1..1000)]):
filter:= proc(n) local L, x;
L:= convert(n, base, 2);
Irreduc(add(L[i]*x^(i-1), i=1..nops(L))) mod 2;
end proc:
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MATHEMATICA
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Select[Prime[Range[2, 100]], !IrreduciblePolynomialQ[bb = IntegerDigits[#, 2]; Sum[bb[[k]] x^(k-1), {k, 1, Length[bb]}], Modulus -> 2]&] (* Jean-François Alcover, Feb 28 2016 *)
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PROG
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(PARI) forprime(p=2, 10^3, if( ! polisirreducible( Mod(1, 2)*Pol(binary(p)) ), print1(p, ", ") ) ); \\ Joerg Arndt, Feb 19 2014
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CROSSREFS
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Cf. A091206 (Primes whose binary expansion encodes a polynomial irreducible over GF(2)), A091212 (Composite, and reducible over GF(2)), A091214 (Composite, but irreducible over GF(2)).
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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