The Shoebox Check, from the bottom of what-if.xkcd.com/108/

The Shoebox Check Number, which appeared in xkcd What-If #108.[1] It is equal to 100010001000×20↑↑↑↑20×S55(1000).[2] It is ill-defined, because the definition includes an unspecified set of functions, the S functions.

What-If #108 concerns the most expensive way to fill a shoebox, and at the bottom, Munroe brings up the idea of writing a check, with a picture of the Shoebox Check.

References

Community content is available under CC-BY-SA unless otherwise noted.