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%I #19 Sep 08 2022 08:45:23
%S 1,2,4,6,8,9,84,288,628
%N Numbers n such that 5^n + n^5 is a semiprime.
%C a(10) >= 868. - _Hugo Pfoertner_, Jul 28 2019
%H <a href="http://factordb.com/index.php?query=5%5E868%2B868%5E5">Status of 5^868-868^5 in factordb.com</a>.
%e 2 is OK because 5^2 + 2^5 = 25 + 32 = 57 = 3*19 (semiprime).
%t Select[Range[100],PrimeOmega[5^# + #^5]==2&] (* _Vincenzo Librandi_, May 21 2014 *)
%o (Magma)IsSemiprime:=func< n|&+[k[2]: k in Factorization(n)] eq 2 >; [n: n in [1..85]|IsSemiprime(5^n+n^5)]; // _Vincenzo Librandi_, Dec 16 2010
%Y Cf. A094133, A114970, A114971, A114974.
%K nonn,more,hard
%O 1,2
%A _Zak Seidov_, Feb 22 2006
%E a(8), a(9) from _Hugo Pfoertner_, Jul 28 2019
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