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 A242339 Numbers k such that k*8^k-1 is semiprime. 1
 3, 6, 9, 13, 21, 24, 32, 45, 61, 62, 73, 132, 150, 174, 187, 217, 266, 331, 534 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The semiprimes of this form are: 1535, 1572863, 1207959551, 7146825580543, 193690812773950291967, 113336795588871485128703, 2535301200456458802993406410751, 1960026433464605549549037738806984897986559, ... LINKS MATHEMATICA Select[Range[80], PrimeOmega[# 8^# - 1]==2&] PROG (MAGMA) IsSemiprime:=func; [n: n in [2..80] | IsSemiprime(s) where s is n*8^n-1]; (PARI) isok(n)=bigomega(n*8^n-1)==2 /* Anders HellstrÃ¶m, Aug 18 2015 */ CROSSREFS Cf. similar sequences listed in A242273. Cf. A064754, A242201. Sequence in context: A153006 A181970 A316531 * A086838 A161669 A128261 Adjacent sequences:  A242336 A242337 A242338 * A242340 A242341 A242342 KEYWORD nonn,more AUTHOR Vincenzo Librandi, May 12 2014 EXTENSIONS a(12)-a(19) from Luke March, Aug 14 2015 STATUS approved

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Last modified September 21 07:06 EDT 2020. Contains 337267 sequences. (Running on oeis4.)