A293537 Numbers k such that (88*10^k - 1)/3 is prime.

0, 1, 3, 6, 9, 121, 153, 172, 378, 496, 841, 1594, 1924, 2692, 4617, 5148, 12891, 24259, 24684, 27690, 68256, 93760, 104989

Offset

1,3

Comments

Numbers k such that the digits 29 followed by k occurrences of the digit 3 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 293w.

Example

3 is in this sequence because (88*10^3 - 1)/3 = 29333 is prime.
Initial terms and associated primes:
a(1) = 0, 29;
a(2) = 1, 293;
a(3) = 3, 29333;
a(4) = 6, 29333333;
a(5) = 9, 29333333333; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(88*10^# - 1)/3] &]

Crossrefs

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

Sequence in context: A196156 A103978 A289064 * A073910 A115251 A057241

Adjacent sequences: A293534 A293535 A293536 * A293538 A293539 A293540

Keyword

nonn,more,hard

Author

Robert Price, Oct 11 2017

Extensions

a(23) from Robert Price, Apr 05 2020

Status

approved