The combination is: 36, 10, 59, 97.

All of them are hidden within the Mansion, if you want to find them they way it's supposed to. In the bottom left room near the entrance, there's a letter on the floor which gives you hints about the whereabouts of 3 of the numbers.

The first one tells about the top of a chest, so just check all the treasure chests again after you opened them (it's the one upstairs near the safe).

The second hint "Behind the Ivory's short of tea and ray" might be hard to understand, but it means the piano on the ground floor (maybe because piano keys are made of ivory? Don't know). Look behind it and you'll read the number on the floor.

The third hint refers to a creaking sound that you can hear once you run over a certain spot near a chair in the right wing on the second floor (you have to listen very carefully to hear it). From this spot, go 5 steps left, 9 steps north, 2 steps left and 6 steps north. Search the floor where you'll read the third number.

The fourth number is acutally written on the letter near the entrance, but it's hidden. When the letter lets you select hints to the first 3 numbers, you can actually select an invisible fourth spot below them which tells you the fourth number.

This is the proper way to aquiring all the numbers.