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Numbers k such that 2^k+5^k is semiprime.
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%I #24 Nov 13 2024 22:22:47

%S 3,6,8,12,14,16,17,19,28,38,47,52,64,101,274,466,1709,2539

%N Numbers k such that 2^k+5^k is semiprime.

%t Select[Range[100],PrimeOmega[2^#+5^#]==2&] (* _James C. McMahon_, Oct 26 2024 *)

%o (Magma)IsSemiprime:=func< n|&+[ k[2]: k in Factorization(n)] eq 2 >;[ n: n in [2..100]|IsSemiprime(2^n+5^n)]; // _Vincenzo Librandi_, Dec 16 2010

%Y Cf. A074600 (2^n + 5^n), A094475 (primes of form 2^k+5^k).

%K nonn,easy

%O 1,1

%A _Zak Seidov_, Oct 19 2006

%E a(14)-a(15) from _D. S. McNeil_, Dec 20 2010

%E a(16)-a(18) from _Sean A. Irvine_, Nov 13 2024