

A294909


Numbers k such that (10^k + 47)/3 is prime.


0



1, 3, 5, 6, 9, 13, 120, 220, 568, 640, 666, 1205, 1600, 2479, 2482, 2939, 3077, 8649, 9520, 12407, 33421, 36162, 41190, 65340
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OFFSET

1,2


COMMENTS

For k > 1, numbers such that k2 occurrences of the digit 3 followed by the digits 49 is prime (see Example section).  Robert Price, Nov 10 2017
a(25) > 2*10^5.  Robert Price, Nov 10 2017


LINKS

Table of n, a(n) for n=1..24.
Makoto Kamada, Factorization of nearrepdigitrelated numbers.
Makoto Kamada, Search for 3w49


EXAMPLE

3 is in this sequence because (10^3 + 47)/3 = 349 is prime.
Initial terms and associated primes:
a(1) = 1, 19;
a(2) = 3, 349;
a(3) = 5, 33349;
a(4) = 6, 333349;
a(5) = 9, 333333349; etc.


MATHEMATICA

Select[Range[0, 100000], PrimeQ[(10^# + 47)/3] &]


PROG

(MAGMA) [n: n in [0..500] IsPrime((10^n+47) div 3)];
(PARI) is(n) = ispseudoprime((10^n + 47) / 3); \\ Altug Alkan, Sep 26 2016


CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
See also similar sequences listed in A274986.
Sequence in context: A096394 A075472 A072522 * A070111 A070117 A176345
Adjacent sequences: A294906 A294907 A294908 * A294910 A294911 A294912


KEYWORD

nonn,more,hard


AUTHOR

Vincenzo Librandi, Sep 26 2016


EXTENSIONS

a(18)a(24) from Robert Price, Nov 10 2017


STATUS

approved



