lean_workbook_plus_79679

Observe this in $\pmod{10}$ . Reduce the 17 to 7 for easier arithmatic. Experiment with the first few powers, and find that $7^{4}\equiv{1}\pmod{10}$ . Now, take $7^{1996}$ and rewrite it as $(7^4)^{499}$ . We now have $1^{499}\equiv{1}\pmod{10}$ . Therefore, the units digit is