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 A239874 Integers k such that 2*k^2 + 1 and 2*k^3 + 1 are prime. 5
 1, 6, 9, 21, 27, 30, 72, 96, 99, 162, 186, 204, 237, 264, 297, 321, 357, 360, 375, 492, 537, 621, 759, 819, 834, 897, 936, 1065, 1242, 1326, 1329, 1359, 1419, 1494, 1506, 1596, 1662, 1704, 1740, 1749, 1761, 1842, 1869, 2157, 2175, 2250, 2274, 2451, 2547 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS All terms > 1 are multiples of 3. Also, no term is congruent to 3 modulo 5. LINKS Zak Seidov, Table of n, a(n) for n = 1..1367 (all terms up to 20000) MATHEMATICA s={1}; Do[If[PrimeQ [2k^2+1]&&PrimeQ[2k^3+1], AppendTo[s, k]], {k, 3, 10^3, 3}]; s Select[Range[3500], PrimeQ[2 #^2 + 1] && PrimeQ[2 #^3 + 1]&] (* Vincenzo Librandi, Mar 29 2014 *) PROG (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 CROSSREFS Intersection of A089001 and A168550. Sequence in context: A355484 A358222 A165717 * A043103 A242756 A268665 Adjacent sequences: A239871 A239872 A239873 * A239875 A239876 A239877 KEYWORD nonn AUTHOR Zak Seidov, Mar 28 2014 STATUS approved

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Last modified August 3 18:16 EDT 2024. Contains 374899 sequences. (Running on oeis4.)