a) Show that ifpandqare distinct odd primes, thenpqis a pseudoprime to the base 2 if and only if $\displaystyle ord_{q}2 \mid (p-1)$ and $\displaystyle ord_{p}2 \mid (q-1)$

b) Use part (a) to decide which of the following integers are pseudoprimes to the base 2: 13*67, 19*73, 23*89, 29*97.