A295627 Numbers k such that (397*10^k + 53)/9 is prime.

5, 9, 17, 47, 54, 75, 191, 207, 267, 894, 2099, 7164, 8625, 10865, 20394, 22251, 23088, 29015, 92369

Offset

1,1

Comments

For k > 1, numbers such that the digits 44 followed by k-1 occurrences of the digit 1 followed by the digit 7 is prime (see Example section).

a(20) > 2*10^5.

Links

Table of n, a(n) for n=1..19.

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

Makoto Kamada, Search for 441w7.

Example

5 is in this sequence because (397*10^5 + 531)/9 = 4411117 is prime.
Initial terms and primes associated:
a(1) = 5, 4411117;
a(2) = 9, 44111111117;
a(3) = 17, 4411111111111111117; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(397*10^# + 53)/9] &]

Crossrefs

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

Sequence in context: A099213 A146067 A336139 * A300128 A334993 A262484

Adjacent sequences: A295624 A295625 A295626 * A295628 A295629 A295630

Keyword

nonn,more,hard

Author

Robert Price, Nov 24 2017

Status

approved