A274914 Numbers k such that 88*10^k + 7 is prime.

1, 2, 3, 4, 8, 14, 17, 19, 24, 26, 30, 43, 81, 85, 171, 267, 282, 2384, 4201, 4450, 6995, 7170, 15049, 15681, 50547, 67691, 109022

Offset: 1

Author

Robert Price, Nov 11 2016

Keywords

• nonn
• more

Comments

For k > 0, numbers k such that the digits 88 followed by k-1 occurrences of the digit 0 followed by the digit 7 is prime (see Example section).

a(28) > 2*10^5.

Examples

			4 is in this sequence because 88*10^4 + 7 = 880007is prime.
Initial terms and associated primes:
a(1) = 1, 887;
a(2) = 2, 8807;
a(3) = 3, 88007;
a(4) = 4, 880007;
a(5) = 8, 8800000007, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 880w7.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[88*10^# + 7] &]

PARI

is(n)=ispseudoprime(88*10^n + 7) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(27) from Robert Price, Mar 17 2020