A294483 Numbers k such that (56*10^k + 403)/9 is prime.

1, 7, 8, 11, 35, 37, 49, 127, 149, 188, 1214, 3020, 5666, 6254, 7874, 8281, 11095, 13831, 20785, 20854, 31249, 40031, 40450, 63100

Offset

1,2

Comments

For k > 1, numbers k such that the digit 6 followed by k - 2 occurrences of the digit 2 followed by the digits 67 is prime (see Example section).

a(25) > 2*10^5.

Links

Table of n, a(n) for n=1..24.

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

Makoto Kamada, Search for 62w67.

Example

1 is in this sequence because (56*10^1 + 403)/9 = 107 is prime.
Initial terms and associated primes:
a(1) = 1, 107;
a(2) = 7, 62222267;
a(3) = 8, 622222267;
a(4) = 11, 622222222267;
a(5) = 35, 622222222222222222222222222222222267; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(56 * 10^# + 403)/9] &]

Crossrefs

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

Sequence in context: A226977 A098731 A348784 * A105740 A377886 A050796

Adjacent sequences: A294480 A294481 A294482 * A294484 A294485 A294486

Keyword

nonn,more,hard

Author

Robert Price, Oct 31 2017

Status

approved