Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #25 Nov 03 2024 18:53:45
%S 1,6,9,21,27,30,72,96,99,162,186,204,237,264,297,321,357,360,375,492,
%T 537,621,759,819,834,897,936,1065,1242,1326,1329,1359,1419,1494,1506,
%U 1596,1662,1704,1740,1749,1761,1842,1869,2157,2175,2250,2274,2451,2547
%N Integers k such that 2*k^2 + 1 and 2*k^3 + 1 are prime.
%C All terms > 1 are multiples of 3. Also, no term is congruent to 3 modulo 5.
%H Zak Seidov, <a href="/A239874/b239874.txt">Table of n, a(n) for n = 1..1367</a> [Duplicate terms removed by _Georg Fischer_, Nov 03 2024]
%p select(t -> isprime(2*t^2+1) and isprime(2*t^3+1), [$1..6000]); # _Robert Israel_, Nov 03 2024
%t s={1};Do[If[PrimeQ [2k^2+1]&&PrimeQ[2k^3+1],AppendTo[s,k]],{k,3,10^3,3}];s
%t Select[Range[3500], PrimeQ[2 #^2 + 1] && PrimeQ[2 #^3 + 1]&] (* _Vincenzo Librandi_, Mar 29 2014 *)
%o (PARI) s=[]; for(n=1, 4000, if(isprime(2*n^2+1) && isprime(2*n^3+1), s=concat(s, n))); s \\ _Colin Barker_, Mar 28 2014
%Y Intersection of A089001 and A168550.
%K nonn
%O 1,2
%A _Zak Seidov_, Mar 28 2014