

A290115


Numbers k such that (7*10^k + 197)/3 is prime.


0



1, 3, 4, 6, 7, 52, 53, 103, 131, 199, 294, 426, 780, 1144, 1876, 2001, 3507, 5737, 6657, 12558, 28303, 31608, 60643, 74741, 124648
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,2


COMMENTS

For k>1, numbers such that the digit 2 followed by k2 occurrences of the digit 3 followed by the digits 99 is prime (see Example section).
a(26) > 2*10^5.


LINKS

Table of n, a(n) for n=1..25.
Makoto Kamada, Factorization of nearrepdigitrelated numbers.
Makoto Kamada, Search for 23w99.


EXAMPLE

4 is in this sequence because (7*10^4 + 197)/3 = 23399 is prime.
Initial terms and primes associated:
a(1) = 1, 89;
a(2) = 3, 2399;
a(3) = 4, 23399;
a(4) = 6, 2333399;
a(5) = 7, 23333399; etc.


MAPLE

select(k > isprime((7*10^k+197)/3), [$1..10000]); # Robert Israel, Jul 20 2017


MATHEMATICA

Select[Range[0, 100000], PrimeQ[(7*10^# + 197)/3] &]


CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A289811 A161001 A168170 * A225794 A206769 A141219
Adjacent sequences: A290112 A290113 A290114 * A290116 A290117 A290118


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Jul 19 2017


EXTENSIONS

a(25) from Robert Price, Jul 17 2018


STATUS

approved



