How many of Jacob's family came into Egypt?

In this blog we will be looking at passages from the Bible and studying them so as to know what God's word for us today would be from what He said long ago.  Today we find ourselves in Genesis 46 where in the Hebrew text of the Old Testament, Biblia Hebraica Stuttgartensia, says that there were 66 (Genesis 46:26)and also that there were 70 (Genesis 46:27).  Another number that is mentioned is that Joseph had two sons born to him in Egypt (Genesis 46:27).  The math seems to be 66 +2 = 70.  Hmmm.  Some would throw their hands up in the air and say the Bible is full of contradictions and be done.  But let's look further.  The Septuagint (LXX) Greek translation, which it seems either Luke or Stephen (Acts 7:14) had in front of him at some time reads 75 persons (having the sons of Rachel numbering not 14 but 18).  This makes the Septuagint version add up thus 33 + 16 + 18 + 7 =75 and 75-9 = 66.  In terms of math, we are drawn to the error of making 74=75 in the septuagint and 68=70 in the Hebrew text.  So what were the author and translator drawing our attention to, assuming that the error would make us look harder.  Er and Onan, Judah's two sons, died.  That could make the equation read 70-2 = 66+2.  But for the case of the Septuagint, 75-9=66, but 33+16+18+7 does not =75.  There is one missing.  Could the Septuagint translator, or the text the translator was using, be drawing our attention to the defiled Dinah, while the Hebrew text is pointing our attention to the death of Judah's sons?  Judah's sons died, as Jacob thought Joseph had died, and right after this Jacob sends Judah ahead of him to Joseph.  What do you think?