What comes next in the sequence; AF, BE CF, DI, FD, ??

Answer --HA

Explanation--

AF =16 (4^2)
BE= 25(5^2)
CF= 36(6^2)
DI = 49(7^2)
FD = 64(8^2)

HA =81(9^2)

Solution -

We will transform the combination of two letters in numbers based on their positioin the alphabet
Therefore, we can write the following:
AF = 16, BE = 25, CF =36 , DI = 49, FD = 64
Now we have the series: ( 16,25,36,49,64,?)
The next number will be: 16 + 9 = 25, 25+11=36, 36+13=49, 49+15=64 , and 64 + 17= 81
81 = HA
The answer is HA