Type superscripts of multiple characters to express mathematical exponents

If in linux I type CTRL-shift-U, followed by a unicode control code, I can type a superscript.

So if I type 10, followed by CTRL-shift-U, followed by b9, I can get 10¹.

How though do I write something like 10 to the power of 18?

Install gucharmap, the GNOME Character Map tool, and find the codepoint number in there. It is always shown as "U+xxxx" (four or more digits).

The codepoint for "superscript 8" is U+2078, from the Superscripts and Subscripts Unicode block. Most superscript digits correspond to U+207x in this block, with the exception of 123 (which are U+00B9, U+00B2, and U+00B3 respectively).

(The reason is that ¹²³ were originally imported from another codepage where they already existed, so they were placed in one of the initial blocks, but all other subscript and superscript numerals were added "fresh" to Unicode so they got their own block. For example, IBM codepage 437 had ² long before Unicode.)

An alternative method is to repurpose one of the keyboard's keys as the Compose key. (For example, if your Caps Lock is entirely unused, you could remap it to Compose.) Afterwards, pressing Compose then Shift^ and 6 would give you ⁶.