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A286959
Positive numbers k such that (10^(k+3)*3277 + 3167)/9 is prime.
0
11, 17, 197, 317, 347, 431, 977, 1949, 1991, 2913, 6317, 9725, 36599
OFFSET
1,1
COMMENTS
Or '364'||...'1'...||'463' in decimal form is prime ('1' concatenated k times to which the prefix '364' and the suffix '463' are concatenated once).
a(1)..a(8) themselves are primes.
EXAMPLE
11 is a term as 36411111111111463 is prime (as a string, it consists of '1' concatenated 11 times to which the prefix '364' and the suffix '463' are concatenated once).
MATHEMATICA
ParallelMap[ If[ PrimeQ[(10^(#+3)*3277+3167)/9], #, Nothing]&, Range[3000]]
PROG
(PARI) is(n)=ispseudoprime((10^(n+3)*3277+3167)/9) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
Sequence in context: A166655 A262552 A279332 * A146446 A228055 A132092
KEYWORD
nonn,hard,more,base
AUTHOR
Mikk Heidemaa, May 17 2017
EXTENSIONS
a(13) from Giovanni Resta, May 25 2017
STATUS
approved