A294121 Numbers k such that (8*10^k - 101)/3 is prime.

2, 3, 4, 5, 6, 17, 53, 95, 156, 228, 261, 323, 363, 1208, 1733, 1744, 2207, 15728, 18196, 50750, 66261, 83811, 156718

Offset

1,1

Comments

For k>1, numbers such that the digit 2 followed by k-2 occurrences of the digit 6 followed by the digits 33 is prime (see Example section).

a(24) > 2*10^5.

Links

Table of n, a(n) for n=1..23.

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

Makoto Kamada, Search for 26w33

Example

3 is in this sequence because (8*10^3 - 101)/3 = 2633 is prime.
Initial terms and primes associated:
a(1) = 2, 233;
a(2) = 3, 2633;
a(3) = 4, 26633;
a(4) = 5, 266633;
a(5) = 6, 2666633; etc.

Mathematica

Select[Range[2, 100000], PrimeQ[(8*10^# - 101)/3] &]

Crossrefs

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

Sequence in context: A116018 A337865 A297181 * A048095 A264975 A031015

Adjacent sequences: A294118 A294119 A294120 * A294122 A294123 A294124

Keyword

nonn,more,hard

Author

Robert Price, Oct 23 2017

Extensions

a(23) from Robert Price, Aug 14 2018

Status

approved