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A100556
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Composite numbers q such that 2^q + q is prime.
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1
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9, 15, 39, 75, 81, 735, 1311, 1881, 3201, 3225, 11795, 88071, 204129, 678561
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OFFSET
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1,1
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LINKS
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Cino Hilliard, Title?. [Dead link]
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EXAMPLE
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For q = 9, 2^9 + 9 = 521, prime.
Note that 2^11795 + 11795 is prime but 11795 is composite and not divisible by 3.
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MATHEMATICA
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Do[If[ !PrimeQ[n] && PrimeQ[2^n + n], Print[n]], {n, 2, 10^6}] (* Ryan Propper, Jul 21 2006 *)
nn=15000; Select[Complement[Range[2, nn], Prime[Range[PrimePi[nn]]]], PrimeQ[2^#+#]&] (* Harvey P. Dale, May 05 2011 *)
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PROG
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(PARI) \ p^q + q is prime q not prime ptoqpq(p, n)= { local(x, y, q); for(q=6, n, if(q%2, if(!isprime(q), y=p^q+q; if(ispseudoprime(y), print(q", "y", ")) ) ) ) }
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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