Your solution to answer is great . However i have other solution to this problem :
10+1^0 =11 , 11+1^1=12 , 12 +1^2 =13 , 13+1^3=14 .... we also have 20+2^0=21 ,21+2^1=23, 23+2^3=31
So my answer is 23 . Hope to see your response soon ! Thanks
