A296093 Numbers k such that (38*10^k + 349)/9 is prime.

0, 2, 3, 8, 27, 30, 39, 141, 387, 626, 972, 1544, 2865, 4371, 5432, 6356, 7545, 9207, 25566, 41313, 41523, 46760, 125166, 187281

Offset

1,2

Comments

For k > 1, numbers such that the digit 4 followed by k-2 occurrences of the digit 2 followed by the digits 61 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 42w61

Example

2 is in this sequence because (38*10^2 + 349)/9 = 461 is prime.
Initial terms and primes associated:
a(1) = 0, 43;
a(2) = 2, 461;
a(3) = 3, 4261;
a(4) = 8, 422222261;
a(5) = 27, 4222222222222222222222222261; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(38*10^# + 349)/9] &]

Crossrefs

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

Sequence in context: A343438 A107704 A246446 * A041399 A183948 A041503

Adjacent sequences: A296090 A296091 A296092 * A296094 A296095 A296096

Keyword

nonn,more,hard

Author

Robert Price, Dec 04 2017

Extensions

a(23)-a(24) from Robert Price, Oct 01 2018

Status

approved