T(N) = 1 + 2*T(N/2)
     = 1 + 2*(1 + 2*T(N/4))
     = 1 + 2 + 4*T(N/4)
-->  = 3 + 4*T(N/4)
     = 3 + 4*(1 + 2*T(N/8))
     = 3 + 4 + 8*T(N/8)
-->  = 7 + 8*T(N/8)
     = 7 + 8*(1 + 2*T(N/16))
     = 7 + 8 + 16*T(N/16)
-->  = 15 + 16*T(N/16)