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A176087
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Numbers n such that (10^n-1)/3 * 10^ceiling(log_10(n+1)) + n is prime.
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3
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OFFSET
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1,2
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COMMENTS
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No term is a multiple of 2, 3, or 5. The decimal expansion of each corresponding prime is n 3's with n's decimal expansion concatenated. Probable primes found by PrimeForm. Prime for 253 proved by Primo. No more terms up to 50000.
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LINKS
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Table of n, a(n) for n=1..3.
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EXAMPLE
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The first term is 1 because 31 is prime.
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PROG
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(PARI) is(n)=ispseudoprime((10^n-1)/3 * 10^logint(10*n, 10) + n) \\ Charles R Greathouse IV, May 22 2017
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CROSSREFS
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Cf. A070746 (n 1's followed by n is prime), A084428 (n 7's followed by n is prime), A174710, A004218.
Sequence in context: A242463 A271985 A255182 * A006060 A077695 A253880
Adjacent sequences: A176084 A176085 A176086 * A176088 A176089 A176090
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KEYWORD
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bref,more,nonn
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AUTHOR
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Rick L. Shepherd, Apr 08 2010
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STATUS
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approved
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