A295837 Numbers k such that (37*10^k + 341)/9 is prime.

1, 2, 4, 7, 10, 11, 17, 20, 65, 70, 811, 947, 1099, 1487, 1540, 6617, 15067, 18433, 19063, 31462, 131270

Offset

1,2

Comments

For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 1 followed by the digits 49 is prime (see Example section).

a(22) > 2*10^5.

Links

Table of n, a(n) for n=1..21.

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

Makoto Kamada, Search for 41w49.

Example

2 is in this sequence because (37*10^2 + 341)/9 = 449 is prime.
Initial terms and associated primes:
a(1) = 1, 79;
a(2) = 2, 449;
a(3) = 4, 41149;
a(4) = 7, 41111149;
a(5) = 10, 41111111149; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(37*10^# + 341)/9] &]

Crossrefs

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

Sequence in context: A153383 A278997 A342782 * A321972 A288482 A177093

Adjacent sequences: A295834 A295835 A295836 * A295838 A295839 A295840

Keyword

nonn,more,hard

Author

Robert Price, Nov 28 2017

Extensions

a(21) from Robert Price, Aug 14 2018

Status

approved