A295322 Numbers k such that (17*10^k - 377)/9 is prime.

3, 19, 27, 145, 166, 196, 247, 345, 370, 799, 1093, 2877, 5223, 9157, 22927, 24600, 25546, 29424, 82540, 95451, 159438

Offset

1,1

Comments

For k > 1, numbers such that the digit 1 followed by k-2 occurrences of the digit 8 followed by the digits 47 is prime (see Example section).

a(22) > 2*10^5.

Links

Table of n, a(n) for n=1..21.

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

Makoto Kamada, Search for 18w47

Example

3 is in this sequence because (17*10^3 - 377)/9 = 1847 is prime.
Initial terms and primes associated:
a(1) = 3, 1847;
a(2) = 19, 18888888888888888847;
a(3) = 27, 1888888888888888888888888847; etc.

Mathematica

Select[Range[2, 100000], PrimeQ[(17*10^# - 377)/9] &]

Prog

(PARI) isok(k) = isprime((17*10^k - 377)/9); \\ Michel Marcus, Nov 20 2017

Crossrefs

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

Sequence in context: A063557 A197541 A273367 * A296934 A062619 A339864

Adjacent sequences: A295319 A295320 A295321 * A295323 A295324 A295325

Keyword

nonn,more,hard

Author

Robert Price, Nov 19 2017

Extensions

a(21) from Robert Price, Mar 24 2018

Status

approved