In Dialog, there’s a general rule that numbers are always treated as numbers, not as dictionary words. This makes parsing more convenient and avoids clogging the game’s dictionary, and applies even when creating words by joining characters together.
However, it does not apply when splitting words apart into their constituent characters. If you split a number, every character is treated as a number; if you split a word, every character is treated as a word, even if it’s actually a number.
For example, if you (split word @a7 into $Chars), you get [@a @7], rather than the expected [@a 7].