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A024912
Numbers k such that 10*k + 1 is prime.
20
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
1,2
FORMULA
a(n) = (A081759(n)+1)/2.
MATHEMATICA
Select[Range[170], PrimeQ[10# + 1] &] (* Ray Chandler, Dec 06 2006 *)
PROG
(Magma) [n: n in [1..1000] |IsPrime(10*n+1)]; // Vincenzo Librandi, Nov 19 2010
(PARI) is(n)=isprime(10*n+1) \\ Charles R Greathouse IV, Jul 02 2013
CROSSREFS
KEYWORD
nonn,easy
STATUS
approved