#PuzzleOfTheDay: If,

2 - 1 => 3
3 - 4 => 7
4 - 9 => 13
5 - 16 => 21
3 - 81 => 0
6 - 25 => ??

https://knowledgezone.co.in/resources/quiz?qId=64847e5d96549a5b219cff67