Task: songer_usc1sect

What follows is an opinion from a United States Court of Appeals.
Your task is to identify the number of the section from the title of the most frequently cited title of the U.S. Code in the headnotes to this case, that is, title 18. In case of ties, code the first to be cited. The section number has up to four digits and follows "USC" or "USCA".

PER CURIAM.
Indicted for, and convicted of, a violation of Section 2421, Title 18 U.S.C., transporting a woman in interstate commerce for the purpose of practicing prostitution, defendant has appealed. Here, putting forward four specifications of error, appellant insists that they are well taken, and, because they are, the judgment must be reversed.
We cannot agree. Indeed, we think it plain that, varying in degree from the inexcusably frivolous claim of point A of the first specification, that the proof fails to show that the so-called victim was a woman, to the little less frivolous one, that the woman could not, because of the claimed marriage to defendant, testify against him in the case, all of the claims of error are wanting in substance and the judgment must be affirmed.
Affirmed.

Question: What is the number of the section from the title of the most frequently cited title of the U.S. Code in the headnotes to this case, that is, title 18? Answer with a number.
Answer:

Answer: 2421