

A294942


Numbers k such that (74*10^k + 313)/9 is prime.


0



0, 2, 6, 15, 18, 26, 51, 75, 86, 114, 257, 275, 537, 753, 914, 1944, 18431, 18741, 21281, 28272, 31002, 71621, 84170, 110961
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OFFSET

1,2


COMMENTS

For k > 1, numbers such that the digit 8 followed by k2 occurrences of the digit 2 followed by the digits 57 is prime (see Example section).
a(25) > 2*10^5.


LINKS

Table of n, a(n) for n=1..24.
Makoto Kamada, Factorization of nearrepdigitrelated numbers.
Makoto Kamada, Search for 82w57.


EXAMPLE

2 is in this sequence because (74*10^2 + 313)/9 = 857 is prime.
Initial terms and primes associated:
a(1) = 0, 43;
a(2) = 2, 857;
a(3) = 6, 8222257;
a(4) = 15, 8222222222222257;
a(5) = 18, 8222222222222222257; etc.


MATHEMATICA

Select[Range[0, 100000], PrimeQ[(74*10^# + 313)/9] &]


PROG

(PARI) isok(k) = isprime((74*10^k + 313)/9); \\ Michel Marcus, Nov 12 2017


CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A020947 A011777 A324176 * A227307 A129631 A014847
Adjacent sequences: A294939 A294940 A294941 * A294943 A294944 A294945


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Nov 11 2017


EXTENSIONS

a(24) from Robert Price, Jun 14 2019


STATUS

approved



