

A294990


Numbers k such that (22*10^k + 257)/9 is prime.


0



1, 3, 4, 6, 22, 31, 201, 265, 340, 388, 396, 561, 1224, 2841, 3234, 3538, 8473, 12061, 29347, 62926, 146029
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OFFSET

1,2


COMMENTS

For k > 1, numbers such that the digit 2 followed by k2 occurrences of the digit 4 followed by the digits 73 is prime (see Example section).
a(22) > 2*10^5.


LINKS

Table of n, a(n) for n=1..21.
Makoto Kamada, Factorization of nearrepdigitrelated numbers.
Makoto Kamada, Search for 24w73


EXAMPLE

3 is in this sequence because (22*10^3 + 257)/9 = 2473 is prime.
Initial terms and primes associated:
a(1) = 1, 53;
a(2) = 3, 2473;
a(3) = 4, 24473;
a(4) = 6, 2444473;
a(5) = 22, 24444444444444444444473; etc.


MATHEMATICA

Select[Range[0, 100000], PrimeQ[(22*10^# + 257)/9] &]


CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A304679 A265735 A038520 * A081888 A306493 A019209
Adjacent sequences: A294987 A294988 A294989 * A294991 A294992 A294993


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Nov 12 2017


EXTENSIONS

a(21) from Robert Price, Jun 08 2018


STATUS

approved



