Det går ikke an
What purpose does "an" serve in this phrase?
It's a bit of a mystery, isn't it? "an" is classified as an adverb in Norwegian, but is actually a German preposition, meaning "on/at/to"which functions as a verb particle in a few set verb phrases adopted from Low German.
It also has an Old Norse counterpart, "á", so it's possible that some of the verb phrases are of Old Norse origin, but I'm not not knowledgeable enough about either of the languages to clarify that.
"å gå an"
"å se an"
"å slå an"
"å legge an på"
"å komme an på"
It's often possible to say "Det går ikke an." without the "an" and still be understood. However, it's traditionally a part of the expression, and it sounds better with the "an". For the other expressions omitting the "an" changes the meaning quite drastically.
While "det går ikke" is used in the same way as "it does not work", "det går ikke an" rather translates to "it is impossible". So it is really just a matter of idioms.
Bonus fact: While speaking, many Norwegians make contractions out of sentences like these and say, "det gåkke an", although you should never write it that way.