A281929 Numbers k such that (19*10^k + 119)/3 is prime.

1, 2, 3, 8, 10, 12, 67, 188, 192, 228, 363, 372, 658, 1748, 1866, 2539, 7897, 10399, 10519, 12872, 14796, 16773, 24736, 30456, 46425, 57316, 65572, 75338

Offset

1,2

Comments

For k>1, numbers such that the digit 6 followed by k-2 occurrences of the digit 3 followed by the digits 73 is prime (see Example section).

a(29) > 2*10^5.

Links

Table of n, a(n) for n=1..28.

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

Makoto Kamada, Search for 63w73.

Example

3 is in this sequence because (19*10^3 + 119)/3 = 6373 is prime.
Initial terms and primes associated:
a(1) = 1, 103;
a(2) = 2, 673;
a(3) = 3, 6373;
a(4) = 8, 633333373;
a(5) = 10, 63333333373; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(19*10^# + 119)/3] &]

Crossrefs

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

Sequence in context: A250037 A360940 A132327 * A286092 A100317 A295030

Adjacent sequences: A281926 A281927 A281928 * A281930 A281931 A281932

Keyword

nonn,more,hard

Author

Robert Price, Feb 11 2017

Status

approved