

A291178


Numbers k such that (13*10^k  37)/3 is prime.


0



1, 2, 4, 7, 8, 26, 64, 116, 123, 157, 178, 288, 328, 1730, 2712, 3244, 3865, 7766, 8792, 9512, 14917, 33912, 39058, 57997, 120306, 150675, 171306, 173467, 175965
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OFFSET

1,2


COMMENTS

For k>1, numbers such that the digit 4 followed by k2 occurrences of the digit 3 followed by the digits 21 is prime (see Example section).
a(30) > 2*10^5.


LINKS

Table of n, a(n) for n=1..29.
Makoto Kamada, Factorization of nearrepdigitrelated numbers.
Makoto Kamada, Search for 43w21.


EXAMPLE

4 is in this sequence because (13*10^4  37)/3 = 43321 is prime.
Initial terms and primes associated:
a(1) = 1, 31;
a(2) = 2, 421;
a(3) = 4, 43321;
a(4) = 7, 43333321;
a(5) = 8, 433333321; etc.


MATHEMATICA

Select[Range[2, 100000], PrimeQ[(13*10^#  37)/3] &]


PROG

(PARI) isok(n) = isprime((13*10^n  37)/3); \\ Altug Alkan, Aug 21 2017


CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A122979 A122980 A012985 * A023145 A094446 A071790
Adjacent sequences: A291175 A291176 A291177 * A291179 A291180 A291181


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Aug 19 2017


EXTENSIONS

a(25)a(29) from Robert Price, Jan 01 2019


STATUS

approved



