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 A143829 Numbers n such that 10n^2 - 1 is prime. 6
 3, 6, 9, 12, 21, 30, 33, 36, 45, 48, 60, 69, 72, 75, 81, 87, 99, 108, 111, 114, 117, 120, 123, 126, 129, 153, 165, 168, 174, 177, 183, 201, 204, 207, 222, 234, 243, 252, 267, 279, 282, 285, 294, 303, 312, 315, 318, 339, 345, 348, 369, 378, 381, 384, 393, 396 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS MATHEMATICA p = 10; a = {}; Do[k = p x^2 - 1; If[PrimeQ[k], AppendTo[a, x]], {x, 1, 1000}]; a PROG (PARI) is(n)=isprime(10*n^2-1) \\ Charles R Greathouse IV, Feb 17 2017 CROSSREFS Sequence in context: A282759 A203016 A153838 * A194420 A277823 A233155 Adjacent sequences:  A143826 A143827 A143828 * A143830 A143831 A143832 KEYWORD nonn AUTHOR Artur Jasinski, Sep 02 2008 STATUS approved

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Last modified December 10 20:38 EST 2019. Contains 329909 sequences. (Running on oeis4.)