"An" can also be used if the first letter is an h and the first syllable is unstressed (an historical event is the example on the Wikipedia page), but, I'm pret

"An" can also be used if the first letter is an h and the first syllable is unstressed (an historical event is the example on the Wikipedia page), but, I'm pretty sure the h in hashing is in a stressed syllable, so that doesn't count either.