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Search: id:A100556
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| A100556 |
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Composite numbers q such that 2^q + q is prime. |
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+0
1
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| 9, 15, 39, 75, 81, 735, 1311, 1881, 3201, 3225, 11795
(list; graph; listen)
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OFFSET
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1,1
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LINKS
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Cino Hilliard, Title?.
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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 (rpropper(AT)stanford.edu), Jul 21 2006
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PROGRAM
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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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Sequence in context: A058505 A133763 A146475 this_sequence A057478 A128687 A146789
Adjacent sequences: A100553 A100554 A100555 this_sequence A100557 A100558 A100559
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KEYWORD
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more,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Jan 12 2005
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EXTENSIONS
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One more term from Ryan Propper (rpropper(AT)stanford.edu), Jul 21 2006
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