google 'factorial' thats not a true factorial but its the same type of pattern and you can probably find it from there. might be easier to google 'n!' which is the generic formula for factorials.
It's not a true factorial because it's not even a factorial at all. A factorial or N! given that N=4 would be the same as multiplying out 4*3*2*1. He doesn't want to multiply anything out he wants to add it up. Which is why you need a Summational formula. But like Kayvee said, work it out in Excel because otherwise you'd have to do it by hand and it'll take too long.
It's not a true factorial because it's not even a factorial at all. A factorial or N! given that N=4 would be the same as multiplying out 4*3*2*1. He doesn't want to multiply anything out he wants to add it up. Which is why you need a Summational formula. But like Kayvee said, work it out in Excel because otherwise you'd have to do it by hand and it'll take too long.