A288151 Numbers k such that 98*10^k - 3 is prime.

1, 5, 7, 8, 13, 20, 33, 39, 43, 51, 91, 113, 119, 132, 208, 411, 525, 581, 931, 1552, 4829, 17537, 40301, 43429

Offset

1,2

Comments

For k>0, numbers such that the digits 97 followed by k-1 occurrences of the digit 9 followed by the digit 7 is prime (see Example section).

a(25) > 2*10^5.

Links

Table of n, a(n) for n=1..24.

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

Makoto Kamada, Search for 979w7.

Example

5 is in this sequence because 98*10^5 - 3 = 9799997 is prime.
Initial terms and primes associated:
a(1) = 1, 977;
a(2) = 5, 9799997;
a(3) = 7, 979999997;
a(4) = 8, 9799999997;
a(5) = 13, 979999999999997; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[98*10^# - 3] &]

Crossrefs

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

Sequence in context: A320391 A047477 A216555 * A242408 A171952 A238011

Adjacent sequences: A288148 A288149 A288150 * A288152 A288153 A288154

Keyword

nonn,more,hard

Author

Robert Price, Jun 05 2017

Status

approved