A285379 Numbers k such that (47*10^k + 133)/9 is prime.

1, 3, 4, 6, 7, 9, 16, 45, 73, 75, 94, 217, 241, 294, 1074, 2133, 2379, 3504, 8241, 16218, 16387, 18135, 31771, 47331, 58456, 72696, 76672

Offset

1,2

Comments

For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 2 followed by the digits 37 is prime (see Example section).

a(28) > 2*10^5.

Links

Table of n, a(n) for n=1..27.

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

Makoto Kamada, Search for 52w37.

Example

4 is in this sequence because (47*10^4 + 133)/9 = 52237 is prime.
Initial terms and associated primes:
a(1) = 1, 67;
a(2) = 3, 5237;
a(3) = 4, 52237;
a(4) = 6, 5222237;
a(5) = 7, 52222237; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(47*10^# + 133)/9] &]

Crossrefs

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

Sequence in context: A094604 A108654 A131530 * A102093 A135215 A092494

Adjacent sequences: A285376 A285377 A285378 * A285380 A285381 A285382

Keyword

nonn,more,hard

Author

Robert Price, Apr 17 2017

Status

approved