cp's OEIS Frontend

A252788 Numbers m such that 3^m + m is a semiprime.

%I A252788 #40 Apr 24 2022 17:21:33
%S A252788 1,4,7,14,16,20,22,32,38,55,80,92,188,220,296,328,370,422,452,454,500,
%T A252788 650,934,962
%N A252788 Numbers m such that 3^m + m is a semiprime.
%C A252788 a(21) >= 500. - _Hugo Pfoertner_, Aug 03 2019
%C A252788 From _Kevin P. Thompson_, Apr 24 2022: (Start)
%C A252788 a(25) >= 1402.
%C A252788 m=1448 is also a term of this sequence. (End)
%H A252788 factordb.com, <a href="http://factordb.com/index.php?query=3%5E500%2B500">Status of 3^500+500</a>.
%H A252788 factordb.com, <a href="http://factordb.com/index.php?id=1100000002718314768">Status of 3^1402+1402</a>.
%e A252788 1 is in this sequence because 3^1+1 = 2*2 is semiprime.
%e A252788 14 is in this sequence because 3^14+14 = 283*16901 and these two factors are prime.
%t A252788 Select[Range[130], PrimeOmega[3^# + #]==2 &]
%o A252788 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..130] | IsSemiprime(s) where s is 3^m+m];
%o A252788 (PARI) first(m)=my(v=vector(m),r=1);for(i=1,m,while(bigomega(3^r + r)!=2,r++);v[i]=r;r++);v; \\ _Anders Hellström_, Aug 14 2015
%Y A252788 Cf. numbers m such that k^m+m is a semiprime: A085745 (k=2), this sequence (k=3), A252789 (k=4), A252790 (k=5), A252791 (k=6), A252792 (k=7), A252793 (k=8), A252794 (k=9), A252795 (k=10).
%Y A252788 Cf. A252656.
%K A252788 nonn,more
%O A252788 1,2
%A A252788 _Vincenzo Librandi_, Dec 22 2014
%E A252788 a(13)-a(16) from _Luke March_, Jul 18 2015
%E A252788 a(17)-a(20) from _Carl Schildkraut_, Aug 19 2015
%E A252788 a(21)-a(24) from _Kevin P. Thompson_, Apr 24 2022