

A294916


Numbers k such that (10^k + 191)/3 is prime.


0



1, 2, 3, 6, 7, 13, 18, 33, 39, 126, 154, 168, 213, 4150, 4153, 5658, 6394, 21993, 29674, 38936, 47095, 94096, 135174, 139398
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OFFSET

1,2


COMMENTS

For k > 1, numbers such that k2 occurrences of the digit 3 followed by the digits 97 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 3w97


EXAMPLE

2 is in this sequence because (10^2 + 191)/3 = 97 is prime.
Initial terms and primes associated:
a(1) = 1, 67;
a(2) = 2, 97;
a(3) = 3, 397;
a(4) = 6, 333397;
a(5) = 7, 3333397; etc.


MATHEMATICA

Select[Range[0, 100000], PrimeQ[(10^# + 191)/3] &]


CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A304709 A183558 A328164 * A233423 A328024 A309815
Adjacent sequences: A294913 A294914 A294915 * A294917 A294918 A294919


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Nov 10 2017


EXTENSIONS

a(23)a(24) from Robert Price, Feb 14 2018


STATUS

approved



