A289535 Numbers k such that (151*10^k - 7)/9 is prime.

1, 4, 6, 12, 13, 15, 18, 30, 49, 72, 799, 832, 877, 1122, 1968, 2046, 8176, 11976, 16444, 20896, 32941, 67027, 94885, 154434

Offset

1,2

Comments

For k > 0, numbers k such that the digits 16 followed by k occurrences of the digit 7 (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 167w.

Example

4 is in this sequence because (151*10^4 - 7)/9 = 167777 is prime.
Initial terms and associated primes:
a(1) = 1, 167;
a(2) = 4, 167777;
a(3) = 6, 16777777;
a(4) = 12, 16777777777777;
a(5) = 13, 167777777777777; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(151*10^# - 7)/9] &]

Crossrefs

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

Sequence in context: A058270 A332934 A058199 * A310592 A310593 A310594

Adjacent sequences: A289532 A289533 A289534 * A289536 A289537 A289538

Keyword

nonn,more,hard

Author

Robert Price, Jul 07 2017

Extensions

a(24) from Robert Price, Jan 08 2020

Status

approved