eshell-number-regexp

eshell-number-regexp is a variable defined in `esh-util.el'.
Its value is

"-?\\([0-9]*\\.\\)?[0-9]+\\(e[-0-9.]+\\)?"

Documentation:
Regular expression used to match numeric arguments.
If `eshell-convert-numeric-arguments' is non-nil, and an argument
matches this regexp, it will be converted to a Lisp number, using the
function `string-to-number'.

You can customize this variable.