A282620 Numbers k such that (67*10^k + 17)/3 is prime.

1, 2, 4, 8, 11, 20, 21, 32, 33, 41, 93, 187, 265, 380, 1088, 1459, 1671, 7328, 11524, 14167, 21719, 47439, 74045

Offset

1,2

Comments

For k>1, numbers such that the digits 22 followed by k-1 occurrences of the digit 3 followed by the digit 9 is prime (see Example section).

a(24) > 2*10^5.

Links

Table of n, a(n) for n=1..23.

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

Makoto Kamada, Search for 223w9.

Example

4 is in this sequence because (67*10^4 + 17)/3 = 223339 is prime.
Initial terms and primes associated:
a(1) = 1, 229;
a(2) = 2, 2239;
a(3) = 4, 223339;
a(4) = 8, 2233333339;
a(5) = 11, 2233333333339; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(67*10^# + 17)/3] &]

Crossrefs

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

Sequence in context: A365922 A180379 A033956 * A320440 A288149 A159693

Adjacent sequences: A282617 A282618 A282619 * A282621 A282622 A282623

Keyword

nonn,more,hard

Author

Robert Price, Feb 19 2017

Status

approved