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I've recently noticed that I keep writing "an 1973 coin", and similarly for all the other dates that start with 1 (e.g. "an 1639 coin").
This does not only apply to coins, obviously, it's just the most common context (in my writing, at least) where an indefinite article comes immediately before a digit numeral. It also does not apply to dates starting with 2 (so "a 2015 coin").
(What's the correct word here for "digit numeral", incidentally?)
It sounds correct in my mind, but I suspect that I might be mentally sounding out digit numerals in my native language (or a form of it) rather than English, and apply the articles based on that.
Can that actually happen, what should I do to prevent it, and what is the correct English form (so that, if needed, I could apply it manually)?