Please read Alexey Sklyarenko's annotations on Pale Fire, Ada and other Nabokov works here.
In VN’s novel Lolita (1955) the number 342 reappears three times. 342 Lawn Street is the address of the Haze house in Ramsdale. 342 is Humbert Humbert's and Lolita's room in The Enchanted Hunters (a hotel in Briceland where they spend their first night together). According to Humbert Humbert, between July 5 and November 18, 1949, he registered (if not actually stayed) at 342 hotels, motels and tourist homes.