A024912 Numbers k such that 10*k + 1 is prime.

1, 3, 4, 6, 7, 10, 13, 15, 18, 19, 21, 24, 25, 27, 28, 31, 33, 40, 42, 43, 46, 49, 52, 54, 57, 60, 63, 64, 66, 69, 70, 75, 76, 81, 82, 88, 91, 94, 97, 99, 102, 103, 105, 106, 109, 115, 117, 118, 120, 123, 129, 130, 132, 136, 138, 145, 147, 148, 151, 153, 157, 160, 162

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• easy

Links

• T. D. Noe, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A030430, A049511, A081759.

Programs

Magma

[n: n in [1..1000] |IsPrime(10*n+1)]; // Vincenzo Librandi, Nov 19 2010

Mathematica

Select[Range[170], PrimeQ[10# + 1] &] (* Ray Chandler, Dec 06 2006 *)

PARI

is(n)=isprime(10*n+1) \\ Charles R Greathouse IV, Jul 02 2013

Formula

a(n) = (A081759(n)+1)/2.