A295824 Numbers k such that (44*10^k - 161)/9 is prime.

1, 3, 4, 10, 81, 135, 217, 232, 247, 250, 325, 579, 955, 1288, 1522, 1839, 2794, 15658, 15777, 54547, 63790

Offset

1,2

Comments

For k > 1, numbers k such that the digit 4 followed by k - 2 occurrences of the digit 8 followed by the digits 71 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 48w71.

Example

3 is in this sequence because (44*10^3 - 161)/9 = 4871 is prime.
Initial terms and associated primes:
a(1) = 1, 31;
a(2) = 3, 4871;
a(3) = 4, 48871;
a(4) = 10, 48888888871; etc.

Mathematica

Select[Range[1, 100000], PrimeQ[(44*10^# - 161)/9] &]

Crossrefs

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

Sequence in context: A288110 A085386 A290517 * A180696 A133760 A335887

Adjacent sequences: A295821 A295822 A295823 * A295825 A295826 A295827

Keyword

nonn,more,hard

Author

Robert Price, Nov 28 2017

Status

approved