HAL was not.
Sexadecimal was first evolution quickly replaced in 60s-late 70s with variants of letters for digits 10-15. MANY variants.
But, HAL was beyond 1st evolution & may even be beyond quantum.
I know, the dates used in the movie were/are already bygone today, yet AH speculated a future to even include my favorite, crystal multi-plane memory chips accessed by laser readers to any given substrate plane! AWESOME.
so, not sexadecimal, but on a better note, the spawn of such.
Real question is, HAL was independent & top AI, electrical, machine that needed no human intervention to achieve what it THOUGHT/AI was the equivalent of human living ability: HAL, sorry, you're an expensive dildoe.
QUICK ADDENDUM EDIT:but a nice one, very nice, our favorite…so PLEASE don't ban us :)