וְאַהֲרֹ֔ן בֶּן־שָׁלֹ֧שׁ וְעֶשְׂרִ֛ים וּמְאַ֖ת שָׁנָ֑ה בְּמֹת֖וֹ בְּהֹ֥ר הָהָֽר׃ (ס)
And Aaron was a hundred and twenty and three years old when he died in mount Hor.
Read kabbalistic (mystical) interpretation of Numbers 33:39: and classical mystical sources.