Why do you need to know? Are you doing your 2017 return?
The most straightforward way would be to get a transcript. Ask for a "Tax Account Transcript" at this IRS webpage for the year ending 12/31/2017.
Note that at the moment, you can get transcripts only online, but this requires that you satisfy the IRS computer that you are who you are - this normally requires that you know some things from your credit report.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"