a(n) = 2^(2^n - 1) + 2^(2^(n + 1) - 1) + 1.A119571a(n) = 2^(2^n - 1) + 2^(2^(n + 1) - 1) + 1.Terms a(0) =4a(1) =11a(2) =137a(3) =32897a(4) =2147516417External referencesoeis: A119571