a(n) = (2^(2^n) + 1 + 2^(2^(n + 1) - 1) + 1)/2.A119572a(n) = (2^(2^n) + 1 + 2^(2^(n + 1) - 1) + 1)/2.Terms a(0) =3a(1) =7a(2) =73a(3) =16513a(4) =1073774593External referencesoeis: A119572