A275538 Numbers k such that (38*10^k + 547)/9 is prime.

1, 3, 4, 9, 10, 13, 19, 21, 25, 28, 70, 81, 97, 106, 291, 369, 460, 577, 4705, 5427, 7153, 7191, 7885, 12070, 20794, 34855

Offset: 1

Author

Robert Price, Aug 01 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 2 followed by the digits 83 is prime (see Example section).

a(27) > 10^5.

Examples

			3 is in this sequence because (38*10^3 + 547)/9 = 4283 is prime.
Initial terms and associated primes:
a(1) = 1, 103;
a(2) = 3, 4283;
a(3) = 4, 42283;
a(4) = 9, 4222222283;
a(5) = 10, 42222222283, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 42w83.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(38*10^# + 547)/9] &]

PARI

isok(n) = isprime((38*10^n + 547)/9); \\ Michel Marcus, Aug 01 2016