A295326 Numbers k such that (182*10^k + 43)/9 is prime.

2, 6, 14, 17, 27, 86, 104, 107, 132, 300, 374, 405, 497, 1179, 1994, 4274, 5252, 17939, 39534, 82898, 85017, 106083

Offset

1,1

Comments

For k > 1, numbers such that the digits 20 followed by k-1 occurrences of the digit 2 followed by the digit 7 is prime (see Example section).

a(23) > 2*10^5.

Links

Table of n, a(n) for n=1..22.

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

Makoto Kamada, Search for 202w7.

Example

2 is in this sequence because (182*10^2 + 43)/9 = 2027 is prime.
Initial terms and primes associated:
a(1) = 2, 2027;
a(2) = 6, 20222227;
a(3) = 14, 2022222222222227;
a(4) = 17, 2022222222222222227;
a(5) = 27, 20222222222222222222222222227; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(182*10^# + 43)/9] &]

Prog

(PARI) isok(k) = isprime((182*10^k + 43)/9); \\ Michel Marcus, Nov 20 2017

Crossrefs

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

Sequence in context: A050859 A245289 A065196 * A032483 A057214 A196445

Adjacent sequences: A295323 A295324 A295325 * A295327 A295328 A295329

Keyword

nonn,more,hard

Author

Robert Price, Nov 19 2017

Extensions

a(22) from Robert Price, Feb 01 2020

Status

approved