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 A242271 Numbers n such that n*8^n+1 is semiprime. 1
 1, 2, 3, 9, 24, 32, 35, 51, 75, 234, 243, 392, 417, 472 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The semiprimes of this form are: 9, 129, 1537, 1207959553, 113336795588871485128705, 2535301200456458802993406410753, ... a(15) >= 483. - Hugo Pfoertner, Aug 05 2019 LINKS factordb.com, Status of 483*8^483+1. MATHEMATICA Select[Range[80], PrimeOmega[# 8^# + 1] == 2 &] PROG (MAGMA) IsSemiprime:=func; [n: n in [1..80] | IsSemiprime(s) where s is n*8^n+1]; CROSSREFS Cf. similar sequences listed in A242203. Cf. A064746, A242178. Sequence in context: A274495 A299705 A318231 * A056198 A143742 A038523 Adjacent sequences:  A242268 A242269 A242270 * A242272 A242273 A242274 KEYWORD nonn,more,hard AUTHOR Vincenzo Librandi, May 10 2014 EXTENSIONS a(10)-a(14) from Hugo Pfoertner and Daniel Suteu, Aug 05 2019 STATUS approved

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Last modified April 20 20:26 EDT 2021. Contains 343137 sequences. (Running on oeis4.)