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%I #8 Mar 09 2017 17:03:59
%S 4,5,9,12,17,20,21,24,32,37,40,45,49,56,57,69,72,77,81,84,85,96,100,
%T 104,105,109,116,117,125,132,136,140,141,145,152,157,164,165,169,172,
%U 181,185,189,192,196,204,205,216,217,220,221,224,245,257,264,269,272,277
%N Numbers n such that 3n(n-1)/2 + 1 is prime.
%H Harvey P. Dale, <a href="/A125603/b125603.txt">Table of n, a(n) for n = 1..1000</a>
%t Select[Range[300],PrimeQ[3# (#-1)/2+1]&] (* _Harvey P. Dale_, Mar 09 2017 *)
%o (PARI) isok(n) = isprime(3*n*(n-1)/2 + 1); \\ _Michel Marcus_, Oct 11 2013
%Y Cf. A005448, A125602.
%K nonn
%O 1,1
%A _Zak Seidov_, Nov 27 2006
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