A271269 Numbers k such that 8*10^k - 49 is prime.

1, 2, 3, 8, 24, 49, 57, 74, 104, 131, 144, 162, 182, 246, 302, 352, 557, 581, 589, 704, 939, 1181, 1937, 2157, 4463, 6013, 7266, 8504, 8691, 16129, 20108, 40677, 74234, 112018

Offset: 1

Author

Robert Price, Apr 03 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 9 followed by the digits 51 is prime (see Example section).

a(35) > 2*10^5.

Examples

			3 is in this sequence because 8*10^3 - 49 = 7951 is prime.
Initial terms and associated primes:
a(1) = 1, 31;
a(2) = 2, 751;
a(3) = 3, 7951;
a(4) = 8, 799999951;
a(6) = 24, 7999999999999999999999951, etc.
		

Links

• Makoto Kamada, Search for 79w51.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[8*10^# - 49] &]

PARI

is(n)=isprime(8*10^n - 49) \\ Charles R Greathouse IV, Feb 16 2017

Extensions

a(34) from Robert Price, Aug 20 2019