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A099190
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Numbers n such that 8*10^n-7 is prime.
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5
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1, 3, 5, 6, 10, 12, 13, 39, 48, 54, 64, 82, 147, 148, 360, 399, 1638, 1876, 2146, 2194, 15789, 23074, 38466, 68400
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OFFSET
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1,2
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COMMENTS
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Also numbers n such that 7*10^n + 9*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Primes of the form 7*10^n+9R_n-6 are the only primes which are one more than twice their reversal.
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LINKS
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FORMULA
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EXAMPLE
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73, 7993, 799993, 7999993, etc. are primes.
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MATHEMATICA
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Do[ If[ PrimeQ[8*10^n - 7], Print[n]], {n, 10000}]
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PROG
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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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