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 A252658 Numbers m such that 5^m - m is a semiprime. 2
 1, 3, 8, 14, 18, 48, 52, 54, 62, 72, 96, 98, 114, 186, 486, 524, 712 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS There are no other known terms under 1000 - the only possible terms are 812 and 908. - Carl Schildkraut, Aug 21 2015 LINKS EXAMPLE 1 is in this sequence because 5^1-1 = 2*2 is semiprime. 18 is in this sequence because 5^18-18 = 199*19169332993 and these two factors are prime. MATHEMATICA Select[Range[100], PrimeOmega[5^# - #]==2 &] PROG (MAGMA) IsSemiprime:=func; [m: m in [1..100] | IsSemiprime(s) where s is 5^m-m]; (PARI) isok(n)=bigomega(5^n - n)==2 \\ Anders HellstrÃ¶m, Aug 21 2015 CROSSREFS Cf. similar sequences listed in A252656. Sequence in context: A063218 A104656 A179993 * A140492 A184517 A028252 Adjacent sequences:  A252655 A252656 A252657 * A252659 A252660 A252661 KEYWORD nonn,more AUTHOR Vincenzo Librandi, Dec 20 2014 EXTENSIONS a(13)-a(17) from Carl Schildkraut, Aug 21 2015 STATUS approved

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Last modified May 13 01:32 EDT 2021. Contains 343829 sequences. (Running on oeis4.)