26594

I choose to start by adding 1, 2 and 3 (1+2+3=6). I noticed that the answer was an even number. I then choose to try it with 14, 15 and 16 (14+15+16=45). I noticed that the answer was an odd number. I did two more sets of numbers:
8+9+10=27
21+22+23=66
I noticed that every time the last number to be added was an even number the answer was odd and if the last number to be added was an odd number the answer was even. These sets of numbers may not be in consecutive order when added but I also noticed that if there are two even numbers in the calculation the answer will be odd and if there are two odd numbers in the calculation the answer will be even.