Have a look at the video on this page: in it mathematicians claim that the sum of 1+2+ 3+4+5+6+7+8+9........ is minus one twelfth.
I don't care who the heck these people are: its crap.
Look at their "proof" : it involves serial sums of numbers that are added in funny ways. This does not prove anything to me, what's worse, the guy at 3:27 moves one serial sum to offset it from the other with no excuse at all and then proceeds to sum them vertically. This is garbage.
Anyone can fiddle with numbers until you get funny stuff like this but it does not make it so.
I am not a mathematician and this sort of crud is the reason why.