if you mean how many times did he shake hands, then the answer is of course 39.
the formula for how to figure out how many hand shakes is as follows.
let me know how I did, or if I was way off base by what you meant by "combinations"
yes there were 39 "shakes", but in which order? he could have shaken hands with #8 or #15 first, #9 or #28 second, and so one. u have the answer. but what about how many orders of shakes in all? so if #1 shook hands with #8 first, #8 also shook hands with #1 first. then #1 shakes hands with #7, so #8 can shake hands with anyone but #1 (already shaken) or # 7 (hes already shaking hands. but maybe if he wants to shake hands with #5, #5s already shaking hands with #12 or #21. so how many combinations in all?