Genesis 5:1..or better put: "Where's Cain?"

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;

2 Male and female created he them; and blessed them, and called their name Adam, in the day when they were created.

3 And Adam lived an hundred and thirty years, and begat a son in his own likeness, and after his image; and called his name Seth:

4 And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters:

Able didn't procreate which explains his absence...but where's Cain?

Simple: Cain was not the son of Adam.