If your father's income --not counting Social Security-- in 2017 was less than $4100 then you could claim him as your dependent for 2017. You would get the personal exemption for claiming a dependent in 2017--that will be $6350 less of your income subject to tax. You cannot claim any other expenses for housing your father.
If you already filed a 2017 return then you can amend it to include your dad as a dependent for 2017.
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