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A265123
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Numbers n such that (2^(n+3) * 5^(n+4) - 1463)/9 is prime (n > 0).
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1
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OFFSET
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1,2
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COMMENTS
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Numbers n such that '393' appended to n times the digit 5 is prime.
Up to a(7) nonprimes alternate with primes; a(9) > 30000 (if it exists).
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LINKS
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EXAMPLE
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1 appears because 5393 is prime.
5 appears because 55555393 ('5' concatenated 5 times and prepended to '393') is prime.
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MAPLE
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A265123:=n->`if`(isprime((2^(n+3) * 5^(n+4) - 1463)/9), n, NULL): seq(A265123(n), n=1..1500);
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MATHEMATICA
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Select[Range[1500], PrimeQ[(2^(# + 3) * 5^(# + 4) - 1463) / 9] &]
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PROG
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(Magma) [n: n in [1..400] | IsPrime((2^(n+3) * 5^(n+4) - 1463) div 9)];
(PARI) is(n)=isprime((2^(n+3)*5^(n+4) - 1463)/9)
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CROSSREFS
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KEYWORD
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nonn,base,hard,more
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AUTHOR
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STATUS
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approved
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