A282280 Numbers k such that 39*10^k + 1 is prime.

4, 6, 12, 14, 18, 26, 40, 46, 114, 138, 194, 484, 889, 939, 1264, 1808, 1964, 2077, 5929, 6512, 8892, 10862, 38120, 53664, 88822

Offset

1,1

Comments

For k>0, numbers such that the digits 39 followed by k-1 occurrences of the digit 0 followed by the digit 1 is prime (see Example section).

a(26) > 10^5.

Links

Table of n, a(n) for n=1..25.

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

Makoto Kamada, Search for 390w1.

Example

6 is in this sequence because 39*10^6 + 1 = 39000001 is prime.
Initial terms and primes associated:
a(1) = 4, 390001;
a(2) = 6, 39000001;
a(3) = 12, 39000000000001;
a(4) = 14, 3900000000000001;
a(5) = 18, 39000000000000000001; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[39*10^# + 1] &]

Crossrefs

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

Sequence in context: A110178 A318712 A140599 * A320495 A047406 A136415

Adjacent sequences: A282277 A282278 A282279 * A282281 A282282 A282283

Keyword

nonn,more,hard

Author

Robert Price, Feb 10 2017

Status

approved