A289811 Numbers k such that (13*10^k + 401)/9 is prime.

1, 3, 4, 6, 7, 15, 18, 57, 75, 82, 358, 1347, 2278, 2577, 4156, 6712, 7471, 14437, 15247, 28251, 62914, 78213, 158694

Offset

1,2

Comments

For k>1, numbers such that the digit 1 followed by k-2 occurrences of the digit 4 followed by the digits 89 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 14w89

Example

3 is in this sequence because (13*10^3 + 401)/9 = 1489 is prime.
Initial terms and primes associated:
a(1) = 1, 59;
a(2) = 3, 1489;
a(3) = 4, 14489;
a(4) = 6, 1444489;
a(5) = 7, 14444489; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(13*10^# + 401)/9] &]

Crossrefs

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

Sequence in context: A093707 A058639 A253888 * A161001 A168170 A290115

Adjacent sequences: A289808 A289809 A289810 * A289812 A289813 A289814

Keyword

nonn,more,hard

Author

Robert Price, Oct 09 2017

Extensions

a(23) from Robert Price, Jan 08 2018

Status

approved