A common pattern I've noticed is for verbs like 行く and 来る after the て form of another verb. I know this is grammatically simply verb listing, but in terms of meaning the verbs often times sort of merge.
For example:
やってくる
入っていく
登っていく
出てくる
I find that in these cases the second verb (くる / いく) is often times written in hiragana instead of kanji. Is this a rule?