Find the pattern, What is the correct answer
Ok, so this question is from seriously hard IQ test that has been doing the rounds on facebook, ok, 17 questions are easy 3 are hellishly hard, The answer to this one is 17, I do not know why, I found out by trial and error just to test, but It's killing me, anyone know why?
Note that $1+3+4+9=17$ and $1+7+1+0=9$.