

A293398


Numbers k such that (728*10^k  71)/9 is prime.


0



0, 2, 5, 6, 11, 14, 41, 47, 51, 84, 164, 228, 293, 1178, 1212, 1292, 2099, 2694, 4446, 7382, 13638, 39428, 40971
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OFFSET

1,2


COMMENTS

For k > 0, numbers such that the digits 80 followed by k1 occurrences of the digit 8 followed by the digit 1 is prime (see Example section).
a(24) > 2*10^5.


LINKS

Table of n, a(n) for n=1..23.
Makoto Kamada, Factorization of nearrepdigitrelated numbers.
Makoto Kamada, Search for 808w1.


EXAMPLE

2 is in this sequence because (728*10^2  71)/9 = 8081 is prime.
Initial terms and primes associated:
a(1) = 0, 73;
a(2) = 2, 8081;
a(3) = 5, 8088881;
a(4) = 6, 80888881;
a(5) = 11, 8088888888881; etc.


MATHEMATICA

Select[Range[0, 100000], PrimeQ[(728*10^#  71)/9] &]


PROG

(PARI) isok(k) = isprime((728*10^k  71)/9); \\ Altug Alkan, Oct 08 2017


CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A135013 A239447 A336527 * A180323 A103035 A088273
Adjacent sequences: A293395 A293396 A293397 * A293399 A293400 A293401


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Oct 08 2017


STATUS

approved



