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A068817
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Numbers n such that n concatenated with n 1's is a prime.
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9
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1, 2, 5, 7, 10, 16, 20, 65, 91, 119, 169, 290, 428, 610, 905, 1051, 3488, 4526, 6445, 8693, 32059
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OFFSET
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1,2
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COMMENTS
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REFERENCES
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Jason Earls, On Smarandache Repunit N Numbers, Smarandache Notions Journal (2004), Vol. 14.1, pp. 251-258.
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LINKS
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EXAMPLE
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5 is a member as 5 followed by five 1's, 511111, is a prime.
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MATHEMATICA
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Do[ If[ PrimeQ[ FromDigits[ Join[IntegerDigits[n], IntegerDigits[(10^n - 1)/9]]]], Print[n]], {n, 1, 1700}]
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PROG
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(PARI) for(n=1, 520, if(isprime(n*10^n+(10^n-1)/9)==1, print1(n, ", ")))
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CROSSREFS
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KEYWORD
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nonn,base,more
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AUTHOR
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EXTENSIONS
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a(18)-a(19) (probable primes) from Jason Earls, Oct 15 2002
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STATUS
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approved
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