Farrah Abraham -- Making it HUGE Off the Back End

Farrah Abraham has money coming out of her ass ... she's raked in sex tape royalties totaling more than $100k in just 2 months!

TMZ broke the story ... the "Teen Mom" turned porn star inked a 6-figure upfront deal with Vivid to sell the XXX tape she shot with James Deen -- "Backdoor Teen Mom."

TMZ has obtained Farrah's first royalty check -- a percentage of profits she receives from sales. So prepare yourself ... after two months, Farrah amassed $119,576.39!!!!

You may recall ... Farah told us on "TMZ Live" ... she's already a millionaire.

Feel free to burn those college degrees in 3 ... 2 ... 1 ...