Seven 0 ......The rule in scripture is natural first, then spiritual. The genealogies in Genesis are given for the natural man first. But Christ does not come out of the firstborn. The line through Seth is the genealogy of Christ and Cain is not a part of that. There are several other examples of this in Genesis. Shem. Abraham, Isaac, Jacob, Judah, and Pharaz are not firstborn.
Seven there is a big difference.
Gen.10:1 Now these are The Generations OF THE SONS OF NOAH, Shem, Ham, and Japheth; and unto them were sons born after the flood.
And it goes on to list them. Now look at that of Cain in Gen.4:17-24. It is nothing like the sons of Noah that were not ancestors of Christ.
Adam's genealogy begins in 5:1:
This is THE BOOK OF THE GENERATIONS OF ADAM. In the day that God created man, in the likeness of God made He him; It goes on, beginning with Seth, (Able was not listed as he was murdered and had no progeny). Cain is conspicuously absent.
This is very different then natural man and firstborn, etc. as in the other genealogies you mentioned. Cain is not a son of Adam.
......Ping