

A290330


Numbers k such that 8*10^k  51 is prime.


0



1, 3, 5, 28, 90, 209, 220, 226, 301, 352, 516, 1746, 2214, 2215, 2364, 2413, 3043, 3895, 5837, 8283, 16551, 20955, 46161, 67302, 82360, 94357, 100439
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OFFSET

1,2


COMMENTS

For k > 1, numbers such that the digit 7 followed by k2 occurrences of the digit 9 followed by the digits 49 is prime (see Example section).
a(28) > 2*10^5.


LINKS

Table of n, a(n) for n=1..27.
Makoto Kamada, Factorization of nearrepdigitrelated numbers.
Makoto Kamada, Search for 79w49.


EXAMPLE

3 is in this sequence because 8*10^3  51 = 7949 is prime.
Initial terms and primes associated:
a(1) = 1, 29;
a(2) = 3, 7949;
a(3) = 5, 799949;
a(4) = 28, 79999999999999999999999999949; etc.


MATHEMATICA

Select[Range[1, 100000], PrimeQ[8*10^#  51] &]


PROG

(PARI) is(n) = ispseudoprime(8*10^n51) \\ Felix FrÃ¶hlich, Aug 12 2019


CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A103526 A054388 A110255 * A300676 A016552 A321069
Adjacent sequences: A290327 A290328 A290329 * A290331 A290332 A290333


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Oct 06 2017


EXTENSIONS

a(27) from Robert Price, Aug 12 2019


STATUS

approved



