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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k > 1, numbers such that the digit 2 followed by k-2 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 near-repdigit-related 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

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Last modified August 14 13:43 EDT 2022. Contains 356117 sequences. (Running on oeis4.)