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A121259 Numbers n such that (3n^2+1)/4 is prime. 1

%I

%S 3,5,7,9,13,19,21,23,27,29,35,47,49,51,55,57,61,65,69,75,77,83,85,91,

%T 97,99,105,111,117,125,127,133,135,149,161,163,173,177,181,183,187,

%U 191,211,217,239,247,251,257,259,273,281,285,295,307,313,315,317,329,331,341

%N Numbers n such that (3n^2+1)/4 is prime.

%F a(n)=(4*A002407(n)-1)/3

%t Select[Range[400],PrimeQ[(3#^2+1)/4]&] (* _Harvey P. Dale_, Mar 24 2011 *)

%o (PARI) is(n)=isprime((3*n^2+1)/4) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. comment by Michael Somos in A002407.

%K nonn,easy

%O 1,1

%A _Zak Seidov_, Aug 23 2006

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Last modified September 20 22:09 EDT 2021. Contains 347592 sequences. (Running on oeis4.)