For centuries. Justification: Jesus was dead for three days: from Friday afternoon (3pm?), day 1, through Saturday, day 2, and into Sunday early morning (6am?), day 3. Total elapsed time 39 hours. Digital computers were around last century (19xx) and this century (20xx), which is two centuries by the same logic. Also two millenia, but I find “centuries” a more satisfying word. Colossus went into operation in 1943, so that’s 80 years elapsed time.
Species 8472 has three legs. Three is an odd number. Four would be an odd number of legs for a member of Species 8472 to have. Three plus four is seven, which is odd (2x3+1). Two odd numbers can therefore add to an odd number.