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 A252657 Numbers m such that 4^m - m is a semiprime. 2
 2, 11, 17, 33, 55, 59, 63, 153, 315 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 549, 721, and 755 are in the sequence, but not necessarily the next three terms. The other possibilities for a(9) are 483, 503, and 543. - Robert Israel, Feb 10 2019 LINKS factordb.com, Status of 4^483-483. EXAMPLE 2 is in this sequence because 4^2-2 = 2*7 is semiprime. 17 is in this sequence because 4^17-17 = 6971*2464477 and these two factors are prime. MATHEMATICA Select[Range[120], PrimeOmega[4^# - #]==2 &] PROG (MAGMA) IsSemiprime:=func; [m: m in [2..120] | IsSemiprime(s) where s is 4^m-m]; CROSSREFS Cf. A024037 (4^n - n). Cf. similar sequences listed in A252656. Sequence in context: A141176 A118839 A091735 * A296053 A234647 A106949 Adjacent sequences:  A252654 A252655 A252656 * A252658 A252659 A252660 KEYWORD nonn,more AUTHOR Vincenzo Librandi, Dec 20 2014 EXTENSIONS a(8)-a(9) from Luke March, Jul 08 2015 STATUS approved

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Last modified May 10 03:11 EDT 2021. Contains 343747 sequences. (Running on oeis4.)