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 A287061 Numbers k such that (10^(k+3)*6319 + 863)/9 is prime (k > 0). 0
 11, 19, 23, 31, 73, 257, 613, 5327, 62359 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The generated prime numbers are of the form '702'||...'1'...||'207' ('1' concatenated k times to which the prefix '702' and the suffix '207' are concatenated once). a(1)..a(7) themselves are primes. a(10) > 80000, if it exists. LINKS Table of n, a(n) for n=1..9. EXAMPLE 11 is a term as (10^(11+3)*6319 + 863)/9 = 70211111111111207 is prime. 23 is a term because (10^(23+3)*6319 + 863)/9 = 70211111111111111111111111207 is prime. MATHEMATICA ParallelMap[ If[ PrimeQ[ (10^(#+3)*6319+863)/9], #, Nothing]&, Range[1000]] PROG (PARI) is(n) = ispseudoprime((10^(n+3)*6319+863)/9); \\ Altug Alkan, Jul 23 2017 CROSSREFS Cf. A032674, A260405, A286916. Sequence in context: A320867 A165947 A129517 * A359401 A161601 A352480 Adjacent sequences: A287058 A287059 A287060 * A287062 A287063 A287064 KEYWORD nonn,base,hard,more AUTHOR Mikk Heidemaa, May 19 2017 STATUS approved

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Last modified July 24 20:07 EDT 2024. Contains 374585 sequences. (Running on oeis4.)