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A217095
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Numbers n such that (10^n + 9^n)/19 is prime.
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13
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OFFSET
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1,1
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COMMENTS
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The numbers n themselves (7, 67, 73, ...) are also prime.
a(7) > 10^5.
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LINKS
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MATHEMATICA
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Select[ Prime[ Range[1, 100000] ], PrimeQ[ (10^# + 9^#)/19 ]& ]
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PROG
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CROSSREFS
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KEYWORD
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hard,nonn,more
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AUTHOR
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STATUS
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approved
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