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A286431 Numbers k such that (22*10^k + 53)/3 is prime. 0
2, 3, 4, 5, 8, 9, 16, 17, 18, 36, 54, 69, 183, 200, 240, 846, 1424, 2511, 4750, 13854, 15414, 103450, 128094, 132746 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 3 followed by the digits 51 is prime (see Example section).

a(25) > 2*10^5.

LINKS

Table of n, a(n) for n=1..24.

Makoto Kamada, Factorization of near-repdigit-related numbers.

Makoto Kamada, Search for 73w51.

EXAMPLE

3 is in this sequence because (22*10^3 + 53)/3 = 7351 is prime.

Initial terms and primes associated:

a(1) = 2, 751;

a(2) = 3, 7351;

a(3) = 4, 73351;

a(4) = 5, 733351;

a(5) = 8, 733333351; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(22*10^# + 53)/3] &]

CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

Sequence in context: A085152 A264886 A287117 * A015931 A330400 A306044

Adjacent sequences:  A286428 A286429 A286430 * A286432 A286433 A286434

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, May 09 2017

EXTENSIONS

a(22)-a(24) from Robert Price, Jul 06 2019

STATUS

approved

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Last modified August 5 01:51 EDT 2021. Contains 346456 sequences. (Running on oeis4.)