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Does anyone have any idea how Arthur Benjamin does all these incredible math “tricks”?(r/math)
Stay away from Numberphile. Numberphile oversimplifies mathematical concepts to the point where they will give you misconceptions about common mathematical notions that will greatly impact your learning later on. I’m noticing this happening a lot with the “1+2+… = -1/12” video because it doesn’t explain that they aren’t using the standard partial sum definition of series convergence.
Not sure how “mathematical” it is, but Secrets of Mental Math is a great, useful book that will help you do really fast calculations in your head.