A282815 Numbers k such that (28*10^k + 131)/3 is prime.

0, 1, 2, 3, 4, 8, 19, 100, 162, 228, 405, 535, 548, 1616, 1982, 2139, 2832, 3115, 3750, 4767, 5051, 9970, 15708, 20909, 33755, 41669, 44822, 45638, 75078

Offset

1,3

Comments

For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 3 followed by the digits 77 is prime (see Example section).

a(30) > 2*10^5.

Links

Table of n, a(n) for n=1..29.

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

Makoto Kamada, Search for 93w77.

Example

3 is in this sequence because (28*10^3 + 131)/3 = 9377 is prime.
Initial terms and associated primes:
a(1) = 0, 53;
a(2) = 1, 137;
a(3) = 2, 977;
a(4) = 3, 9377;
a(5) = 4, 93377; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(28*10^# + 131)/3] &]

Crossrefs

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

Sequence in context: A102276 A215897 A276673 * A339630 A105055 A108506

Adjacent sequences: A282812 A282813 A282814 * A282816 A282817 A282818

Keyword

nonn,more,hard,changed

Author

Robert Price, Feb 23 2017

Status

approved