R. Joshua b. Levi said: One who sees a friend after a lapse of thirty days says: Blessed is He who has kept us alive and preserved us and brought us to this season.* If after a lapse of twelve months he says: Blessed is He who revives the dead.**
— Babylonian Talmud, Berakhot 58b
— * “Shehecheyanu,” for short [full blessing text]
— ** Kolel: The Adult Centre for Adult Jewish Learning presents both blessings as outlined in Berakhot 58b and another option for blessing upon seeing a long-lost friend.