This is the 6942nd most frequent Russian word.
андресу
It appears that "андресу" is not a standard Russian word. It may be a misspelling or transliteration issue. Could you clarify or provide context?
The word 'андресу' is used as a proper noun in the dative case to indicate the recipient of the letter.
Я отправлю письмо Андресу.
I will send a letter to Andres.
Here, 'андресу' is again in the dative case, following the preposition 'к' to express the direction of the visit.
Мы поехали в гости к Андресу.
We went to visit Andres.
In this sentence, 'андресу' is in the dative case, associated with the verb of attention to indicate the person towards whom the focus is directed.