A271360 Numbers k such that 5*10^k + 87 is prime.

1, 2, 3, 4, 6, 16, 38, 39, 46, 61, 62, 100, 116, 152, 190, 298, 472, 642, 688, 1676, 1971, 2338, 4389, 4520, 4986, 7765, 9428, 10820, 18984, 19797, 35360, 42146, 168807

Offset: 1

Author

Robert Price, Apr 05 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 87 is prime (see Example section).

a(34) > 2*10^5.

Examples

			3 is in this sequence because 5*10^3 + 87 = 5087 is prime.
Initial terms and associated primes:
a(1) = 1, 137;
a(2) = 2, 587;
a(3) = 3, 5087;
a(4) = 4, 50087;
a(5) = 6, 5000087, etc.
		

Links

• Makoto Kamada, Search for 50w87.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[5*10^# + 87] &]

PARI

is(n)=ispseudoprime(5*10^n + 87) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(33) from Robert Price, Feb 24 2019