a(n) = 1 - 2^(2^n) + 2^(2^(n+1)).A220294a(n) = 1 - 2^(2^n) + 2^(2^(n+1)).Terms a(0) =3a(1) =13a(2) =241a(3) =65281a(4) =4294901761External referencesoeis: A220294