A282278 Numbers k such that (22*10^k + 161)/3 is prime.

0, 1, 2, 4, 5, 6, 7, 13, 28, 36, 40, 74, 233, 425, 828, 888, 1970, 2119, 2338, 2971, 3030, 14005, 20190, 29589, 47034, 47292, 51457, 64326, 70259, 90110, 120828, 122681

Offset

1,3

Comments

For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 3 followed by the digits 87 is prime (see Example section).

a(33) > 2*10^5.

Links

Table of n, a(n) for n=1..32.

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

Makoto Kamada, Search for 73w87.

Example

4 is in this sequence because (22*10^4 + 161)/3 = 73387 is prime.
Initial terms and primes associated:
a(1) = 0, 61;
a(2) = 1, 127;
a(3) = 2, 787;
a(4) = 4, 73387;
a(5) = 5, 733387; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(22*10^# + 161)/3] &]

Crossrefs

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

Sequence in context: A276005 A092058 A134532 * A268448 A230581 A361825

Adjacent sequences: A282275 A282276 A282277 * A282279 A282280 A282281

Keyword

nonn,more,hard

Author

Robert Price, Feb 10 2017

Extensions

a(31)-a(32) from Robert Price, May 04 2019

Status

approved