A122116 Numbers k such that 2^k+5^k is semiprime.
3, 6, 8, 12, 14, 16, 17, 19, 28, 38, 47, 52, 64, 101, 274, 466, 1709, 2539
Offset: 1
Programs
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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
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Mathematica
Select[Range[100],PrimeOmega[2^#+5^#]==2&] (* James C. McMahon, Oct 26 2024 *)
Extensions
a(14)-a(15) from D. S. McNeil, Dec 20 2010
a(16)-a(18) from Sean A. Irvine, Nov 13 2024