A294375 Numbers k such that (16*10^k + 41)/3 is prime.

0, 1, 2, 3, 6, 7, 8, 12, 17, 272, 315, 405, 560, 728, 919, 1578, 1608, 4736, 7751, 18332, 22787, 50005, 69265, 91032, 92591, 148071, 168181

Offset

1,3

Comments

For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 3 followed by the digits 47 is prime (see Example section).

a(28) > 2*10^5.

Links

Table of n, a(n) for n=1..27.

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

Makoto Kamada, Search for 53w47.

Example

2 is in this sequence because (16*10^2 + 41)/3 = 547 is prime.
Initial terms and associated primes:
a(1) = 0, 19;
a(2) = 1, 67;
a(3) = 2, 547;
a(4) = 3, 5347;
a(5) = 6, 5333347; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(16*10^# + 41)/3] &]

Crossrefs

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

Sequence in context: A072426 A189137 A230548 * A166458 A189013 A242940

Adjacent sequences: A294372 A294373 A294374 * A294376 A294377 A294378

Keyword

nonn,more,hard

Author

Robert Price, Oct 29 2017

Extensions

a(26)-a(27) from Robert Price, Mar 13 2019

Status

approved