Number reasoning, the most difficult problem in the world

Number reasoning, the most difficult problem in the world

It should be 42
The latter is the sum of the squares of the digits of the former
For example, 16 = 4 square
37 = 1 square + 6 square
58 = 3 square + 7 square
wait
therefore
Next: 1 square + 4 square + 5 square = 42
Next: 4 square + 2 square = 20
Next: 2 square = 4
Further down the loop