Genesis 5:4

And the days of Adam, after he had begotten Seth, were
eight hundred years
The Septuagint version is seven hundred; for having added one hundred years more the should be, to the years of his life before the birth of Seth, here they are taken away to make the number of his years complete: and he begat sons and daughters;
not only after the birth of Seth, but before, though we have no account of any, unless of Cain's wife; but what their number was is not certain, either before or after; some say he had thirty children, besides Cain, Abel, and Seth; and others a hundred ^F3. Josephus says the number of children, according to the old tradition, was thirty three sons and twenty three daughters. ^F4 (These families had at least five children, for one son is named as well as other sons and daughters. Therefore there must be at least three sons and two daughters in each family. For a family to have at least three sons and two daughters, according to the laws of chance, a family must on the average have nine children for this to be a near certainty. Hence the families listed in this chapter must have been large by today's standards. Given their long life, this is not at all unusual. However even today, the Old Order Mennonites of Waterloo County in Ontario and Lancaster County in Pennsylvannia, have many families this large. Ed.)