Here's my basic calculation:
at the time of Yetzias Metzrayim (Exodus), the 600K males had 5 kids per family (Targum Yonasan)
half of the kids were males
(it is also highly probable that even if they hadn't they would have on average 5 kids in the first 20 years).
That totals to 1.5M boys (not counting Levis). They turned men 20-60 years in the next 40 years of wandering in the desert. Some casualties here (24K at G.Calf) and there (Midyan) do not add up to 900K.
I would expect the population to count at least 1.5M males at the time of entering the promised Land. The Torah only accounts for around 630K.
What am I missing?