A295608 Numbers k such that (29*10^k + 223)/9 is prime.

2, 5, 9, 11, 23, 27, 33, 111, 119, 314, 375, 551, 1694, 3413, 3495, 4172, 9287, 10412, 179697

Offset

1,1

Comments

For k > 1, numbers such that the digit 3 followed by k-2 occurrences of the digit 2 followed by the digits 47 is prime (see Example section).

a(20) > 2*10^5.

Links

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

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

Makoto Kamada, Search for 32w47

Example

2 is in this sequence because (29*10^2 + 223)/9 = 347 is prime.
Initial terms and primes associated:
a(1) = 2, 347;
a(2) = 5, 322247;
a(3) = 9, 3222222247;
a(4) = 11, 322222222247;
a(5) = 23, 322222222222222222222247; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(29*10^# + 223)/9] &]

Prog

(PARI) isok(k) = isprime((29*10^k + 223)/9); \\ Michel Marcus, Nov 24 2017

Crossrefs

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

Sequence in context: A347305 A343878 A057471 * A349048 A099434 A191104

Adjacent sequences: A295605 A295606 A295607 * A295609 A295610 A295611

Keyword

nonn,more,hard

Author

Robert Price, Nov 24 2017

Extensions

a(19) from Robert Price, Sep 08 2018

Status

approved