A295971 Numbers k such that (46*10^k + 143)/9 is prime.

1, 8, 20, 28, 40, 41, 71, 208, 263, 346, 455, 743, 878, 920, 1451, 2980, 4678, 7748, 13301, 106343, 170932

Offset

1,2

Comments

For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 1 followed by the digits 27 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 51w27.

Example

8 is in this sequence because (46*10^8 + 143)/9 = 511111127 is prime.
Initial terms and associated primes:
a(1) = 1, 67;
a(2) = 8, 511111127;
a(3) = 20, 511111111111111111127;
a(4) = 28, 51111111111111111111111111127;
a(5) = 40, 51111111111111111111111111111111111111127; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(46*10^# + 143)/9] &]

Prog

(PARI) isok(k) = isprime((46*10^k + 143)/9); \\ Michel Marcus, Dec 01 2017

Crossrefs

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

Sequence in context: A110116 A373494 A373473 * A317760 A022757 A246308

Adjacent sequences: A295968 A295969 A295970 * A295972 A295973 A295974

Keyword

nonn,more,hard

Author

Robert Price, Nov 30 2017

Extensions

a(20)-a(21) from Robert Price, Jan 17 2019

Status

approved