A Mathematical Puzzle

Here is a puzzle; not much difficult, just some thinking and some analysis of what is given to get answer; try your way. I shall give the solution in my post on March 30, if nobody could solve it. You can post your solutions as comment. So here it is : If

1 * 2 = 5
3 * 4 = 25
5 * 6 = 61
7 * 8 = 113
then,
9 * 10 = ?


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