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A157979
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Least nonnegative k such that 3^(2^n)+k is prime.
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1
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0, 2, 2, 2, 26, 70, 92, 190, 788, 436, 86, 3032, 13622, 2810, 7562, 33172, 16942
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OFFSET
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0,2
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COMMENTS
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The associated primes are in A157980.
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LINKS
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FORMULA
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a(n) = Min{k=>0 such that 3^(2^n))+k is prime} = Min{k=>0 such that A000244(A000079(n))+k is in A000040}.
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EXAMPLE
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a(0) = 0 because 3^2^0 + 0 = 3^1 + 0 = 3 is prime. a(1) = 2 because 3^2^1 + 2 = 3^2 + 0 = 3 is prime. a(2) = 2 because 3^4 + 2 = 83 is prime. a(3) = 2 because 3^8 + 2 = 6563 is prime. a(4) = 26 because 3^16 + 26 = 43046747 is prime. a(5) = 70 because 3^32 + 2 = 1853020188851911 is prime. a(6) = 92 because 3^64 + 2 = 3433683820292512484657849089373 is prime.
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PROG
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(PARI) { a(n) = nextprime( 3^(2^n) ) - 3^(2^n) } \\ Max Alekseyev, Sep 13 2009
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CROSSREFS
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KEYWORD
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more,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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