If you were covered by a retirement plan up to September 2017, you are considered as covered by a retirement plan in 2017, even if you were not covered from October to December 2017.
You can still deduct an IRA contribution if your Modified Gross Adjusted Income is below a certain level depending on your filing status.
Please read this IRS document to see if you are eligible for an IRA deduction:
https://www.irs.gov/retirement-plans/2017-ira-deduction-limits-effect-of-modified-agi-on-deduction-i...
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