It is: 1225+39 = 1264
The sum (done on a spreadsheet) of 1 to 35 as odd numbers is 1225.
The sum of -18 and 39 is 21.
39.
89
By the uniqueness of integers, the only integer for 39 is 39 itself. And that cannot have a sum of 3.
The 3rd magic sum in the 39 clues game is 42.
The answer is 39.
It is: 127+39+262 = 428
18
41
123
66