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A239874
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Integers k such that 2*k^2 + 1 and 2*k^3 + 1 are prime.
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5
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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
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OFFSET
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1,2
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COMMENTS
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All terms > 1 are multiples of 3. Also, no term is congruent to 3 modulo 5.
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LINKS
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MATHEMATICA
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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 *)
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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