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 A268574 Numbers n such that (2^n+1)^2-2 is a semiprime. 1
 4, 6, 7, 10, 11, 14, 22, 36, 38, 39, 44, 45, 48, 49, 60, 72, 74, 75, 89, 92, 96, 99, 105, 110, 111, 113, 116, 131, 138, 143, 150, 170, 173, 182, 194, 201, 212, 234, 260 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(40) >= 282. - Hugo Pfoertner, Aug 05 2019 LINKS factordb.com, Status of (2^282+1)^2-2. EXAMPLE a(1) = 4 because 17^2-2 = 287 = 7*41, which is semiprime. a(2) = 6 because 65^2-2 = 4223 = 41*103, which is semiprime. MATHEMATICA Select[Range[105], PrimeOmega[(2^# + 1)^2 - 2] == 2 &] PROG (MAGMA) IsSemiprime:=func; [n: n in [1..110]| IsSemiprime(s) where s is (2^n+1)^2-2]; (PARI) isok(n) = bigomega((2^n+1)^2-2) == 2; \\ Michel Marcus, Feb 22 2016 CROSSREFS Cf. A091513, A091514, A093069, A269264. Sequence in context: A032785 A096887 A340161 * A023631 A080641 A272632 Adjacent sequences:  A268571 A268572 A268573 * A268575 A268576 A268577 KEYWORD nonn,more,hard AUTHOR Vincenzo Librandi, Feb 21 2016 EXTENSIONS a(25)-a(39) from Hugo Pfoertner, Aug 05 2019 STATUS approved

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Last modified August 7 23:50 EDT 2022. Contains 355995 sequences. (Running on oeis4.)