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 A176087 Numbers n such that (10^n-1)/3 * 10^ceiling(log_10(n+1)) + n is prime. 3
 1, 253, 35473 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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. LINKS Table of n, a(n) for n=1..3. EXAMPLE The first term is 1 because 31 is prime. PROG (PARI) is(n)=ispseudoprime((10^n-1)/3 * 10^logint(10*n, 10) + n) \\ Charles R Greathouse IV, May 22 2017 CROSSREFS 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 KEYWORD bref,more,nonn AUTHOR Rick L. Shepherd, Apr 08 2010 STATUS approved

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Last modified March 3 16:27 EST 2024. Contains 370512 sequences. (Running on oeis4.)