Let the two 17 bit numbers be,
(a0 a1 a2 a3....a16)
(b0 b1 b2.........b16)
1 half adder will take input a16, b16 and return a sum and a carry. This carry will be forwarded to the next adder (full adder). The first full adder will take three inputs (the carry from previous stage, a15, b15) and generate the next sum and next carry for the second full adder. In this way, 16 full adders are used.
So, 1 H.A and 16 F.A (ans)