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A295826 Numbers k such that (202*10^k - 13)/9 is prime. 0
1, 2, 4, 20, 22, 34, 35, 41, 185, 547, 644, 713, 1489, 1885, 3211, 3257, 3625, 6733, 47732 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k > 0, numbers such that the digits 22 followed by k-1 occurrences of the digit 4 followed by the digit 3 is prime (see Example section).

a(20) > 10^5.

LINKS

Table of n, a(n) for n=1..19.

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

Makoto Kamada, Search for 224w3

EXAMPLE

2 is in this sequence because (202*10^2 - 13)/9 = 2243 is prime.

Initial terms and primes associated:

a(1) = 1, 223;

a(2) = 2, 2243;

a(3) = 4, 224443;

a(4) = 20, 2244444444444444444443;

a(5) = 22, 224444444444444444444443; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(202*10^# - 13)/9] &]

CROSSREFS

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

Sequence in context: A178223 A033180 A215815 * A201502 A069535 A108866

Adjacent sequences:  A295823 A295824 A295825 * A295827 A295828 A295829

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 28 2017

STATUS

approved

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Last modified November 18 04:44 EST 2019. Contains 329248 sequences. (Running on oeis4.)