If high school memories serve, Latin has regular number-names for 11 through 17, but then semi-irregular ones for 18 (duodeviginti, or "two from twenty") and 19

If high school memories serve, Latin has regular number-names for 11 through 17, but then semi-irregular ones for 18 (duodeviginti, or "two from twenty") and 19 (undeviginti, "one from twenty"). (I say semi-irregular because they're inconsistent with 11 through 17, but at least consistent with each other, unlike say "eleven" and "twelve", as far as I can tell.)