A124198 Numbers k such that 21*k + 1 is prime.
2, 6, 10, 16, 18, 20, 22, 26, 30, 32, 36, 42, 46, 48, 50, 52, 62, 68, 70, 76, 82, 92, 96, 102, 108, 110, 116, 120, 126, 128, 130, 136, 146, 148, 158, 160, 168, 170, 172, 176, 178, 182, 186, 198, 200, 202, 206, 220, 222, 228, 230, 236, 238, 246, 248, 258, 262, 278
Offset: 1
Examples
If k=148 then 21*k + 1 = 3109 (prime).
Links
- Harvey P. Dale, Table of n, a(n) for n = 1..1000
Programs
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Magma
[n: n in [0..300] | IsPrime(21*n + 1)] // Vincenzo Librandi, Mar 26 2010
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Mathematica
Select[Range[300],PrimeQ[21#+1]&] (* Harvey P. Dale, Mar 08 2016 *)
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PARI
is(n)=isprime(21*n+1) \\ Charles R Greathouse IV, Jun 06 2017