Having seen it written on a blackboard in the Simpsons, I wanted to check if

3987^{12} + 4365^{12} = 4472^{12}

thus disproving 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