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A252794 Numbers m such that 9^m + m is a semiprime. 1

%I

%S 1,5,68,85,86,92,136

%N Numbers m such that 9^m + m is a semiprime.

%C a(8) > 435. - _Carl Schildkraut_, Aug 14 2015

%e 1 is in this sequence because 9^1+1 = 2*5 is semiprime.

%e 5 is in this sequence because 9^5+5 = 2*29527 and these two factors are prime.

%t Select[Range[435], PrimeOmega[9^# + #]==2 &]

%o (MAGMA) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..435] | IsSemiprime(s) where s is 9^m+m];

%Y Cf. similar sequences listed in A252788.

%Y Cf. A252662.

%K nonn,more

%O 1,2

%A _Vincenzo Librandi_, Dec 27 2014

%E a(4)-a(7) from _Carl Schildkraut_, Aug 14 2015

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Last modified October 1 08:39 EDT 2020. Contains 337442 sequences. (Running on oeis4.)