This Bible contradiction is from the Skeptic's Annotated Bible.
Absalom had no sons.
2 Samuel 18:18 View context
Now Absalom in his lifetime had taken and reared up for himself a pillar, which [is] in the king's dale: for he said, I have no son to keep my name in remembrance: and he called the pillar after his own name: and it is called unto this day, Absalom's place.
Absalom had three sons.
2 Samuel 14:27 View context
And unto Absalom there were born three sons, and one daughter, whose name [was] Tamar: she was a woman of a fair countenance.