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A295403 Numbers k such that (41*10^k - 383)/9 is prime. 0
1, 3, 5, 6, 21, 39, 114, 239, 246, 348, 906, 1115, 2801, 2958, 2982, 4275, 6581, 8736, 27051, 115523, 124335 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k > 1, numbers such that the digit 4 followed by k-2 occurrences of the digit 5 followed by the digits 13 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 45w13

EXAMPLE

3 is in this sequence because (41*10^3 - 383)/9 = 4513 is prime.

Initial terms and primes associated:

a(1) = 1, 3;

a(2) = 3, 4513;

a(3) = 5, 455513;

a(4) = 6, 4555513;

a(5) = 21, 4555555555555555555513; etc.

MATHEMATICA

Select[Range[1, 100000], PrimeQ[(41*10^# - 383)/9] &]

PROG

(PARI) isok(k) = isprime((41*10^k - 383)/9); \\ Michel Marcus, Nov 22 2017

CROSSREFS

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

Sequence in context: A050563 A282809 A168156 * A272440 A276704 A103022

Adjacent sequences:  A295400 A295401 A295402 * A295404 A295405 A295406

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 21 2017

EXTENSIONS

a(20)-a(21) from Robert Price, Nov 16 2018

STATUS

approved

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Last modified October 21 22:47 EDT 2019. Contains 328315 sequences. (Running on oeis4.)