A124204 Numbers k such that 20*k + 1 is prime.

2, 3, 5, 9, 12, 14, 20, 21, 23, 26, 27, 30, 32, 33, 35, 38, 41, 44, 47, 51, 53, 59, 60, 65, 66, 68, 69, 74, 80, 81, 86, 87, 90, 93, 95, 104, 107, 108, 111, 114, 117, 119, 122, 126, 131, 137, 140, 143, 150, 152, 153, 156, 159, 161, 165, 168, 173, 177, 179, 185, 188, 191

Offset: 1

Author

Parthasarathy Nambi, Dec 07 2006

Keywords

• nonn
• easy

Examples

			If k=95 then 20*k + 1 = 1901 (prime).
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Programs

Magma

[n: n in [0..6000] | IsPrime(20*n + 1)]; // Vincenzo Librandi, Mar 26 2010

Mathematica

Select[Range[200],PrimeQ[20#+1]&] (* Harvey P. Dale, Mar 19 2025 *)

PARI

is(n)=isprime(20*n+1) \\ Charles R Greathouse IV, Jun 13 2017