Having seen it written on a blackboard in the Simpsons, I wanted to check if 398712 + 436512 = 447212 thus disproving [Fermat’s Last Theorem](http://en.wikipedia.org/wiki/Fermat's_Last_Theorem). My pocket calculator confirmed the expression to be true, but those are big numbers, and the calculator lacks precision. This seemed like a perfect opportunity to use calc mode. `M-x calc ` to enter calc mode First enter the left hand side ``` 3987 <Enter> 12 ^ 4365 <Enter> 12 ^ ``` Both numbers are now there in the stack: ``` --- Emacs Calculator Mode --- 2: 16134474609751291283496491970515151715346481 1: 47842181739947321332739738982639336181640625 ``` Hit `+` to add them together. Now to enter the right hand side. ``` 4472 <Enter> 12 ^ ``` Now the left and right sides of the original expression are there in the stack, and you can see that whilst they may be sufficiently equal to fool a pocket calculator, they can’t fool Emacs. ``` \--- Emacs Calculator Mode --- 2: 63976656349698612616236230953154487896987106 1: 63976656348486725806862358322168575784124416 ``` Hit `-` to see the difference: ``` 1211886809373872630985912112862690 ``` `d g` to group the number, then hit `y` to yank the number back into the current buffer. ``` 1,211,886,809,373,872,630,985,912,112,862,690 ``` … as I just did there. ## See Also - [[Calc Mode 1 Binary Numbers]] - [[Calc Mode 2 Two’s Complement]]