Should I add my contribution to OEIS in my CV?
Yes, but do try to say more about it than just, "I contributed A345317 to the OEIS." Surely some research has gone into its discovery, so describe that in brief. Because, that will determine how interesting and relevant your addition to the OEIS appears in the eyes of whoever reads your CV.
The impact of your contribution might also depend on your level. A contribution by a high-school student would be intriguing, so I would strongly recommend putting it on your CV. If you're an under-grad or grad student, it would still be worth putting on your CV, but I would expect to see the surrounding research highlighted more than the bare bones of your contribution.