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%I #11 Sep 08 2022 08:46:10
%S 2,7,9,111,129,133,361
%N Numbers m such that 8^m - m is a semiprime.
%C a(8) >= 369. - _Hugo Pfoertner_, Aug 03 2019
%H factordb.com, <a href="http://factordb.com/index.php?query=8%5E369-369">Status of 8^369-369</a>.
%e 2 is in this sequence because 8^2-2 = 2*31 is semiprime.
%e 9 is in this sequence because 8^9-9 = 23*5835553 and these two factors are prime.
%t Select[Range[70],PrimeOmega[8^# - #]==2 &]
%o (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..70] | IsSemiprime(s) where s is 8^m-m];
%Y Cf. similar sequences listed in A252656.
%K nonn,more,hard
%O 1,1
%A _Vincenzo Librandi_, Dec 21 2014
%E a(4)-a(7) from _Hugo Pfoertner_, Aug 03 2019
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