"You Know My Name (Look Up the Number)" is a song by the Beatles originally released as the B-side of the single "Let It Be" on 6 March 1970. Although first issued with their final single (penultimate single in the United States), it was recorded in four separate sessions beginning with three in May and June 1967, and one in 1969.

The song is a music hall comedy number. Lennon came up with the lyric/title after seeing a phone book. He said:

That was a piece of unfinished music that I turned into a comedy record with Paul. I was waiting for him in his house, and I saw the phone book was on the piano with 'You know the name, look up the number.' That was like a logo, and I just changed it.

McCartney once told Beatles recording analyst Mark Lewisohn, "[People] are only just discovering things like 'You Know My Name (Look Up the Number)' — probably my favourite Beatles' track!" He went on to explain:

It's so insane. All the memories ... I mean, what would you do if a guy like John Lennon turned up at the studio and said, 'I've got a new song'. I said, 'What's the words?' and he replied 'You know my name look up the number'. I asked, 'What's the rest of it?' 'No, no other words, those are the words. And I want to do it like a mantra!'

The lounge section includes a reference to Denis O'Dell, associate producer on the A Hard Day's Night film, whom Lennon had also worked with on How I Won the War. Partway through the song, Lennon introduces McCartney as lounge singer "Denis O’Bell." The reference prompted numerous telephone calls to O'Dell's home by fans who told him, "We have your name and now we've got your number," as well as personal visits by fans wanting to live with him.

The song is in the key of D and begins with a I–I6-IV–V⁷–I-I6–IV–V⁷–I chord progression: thus "You know" involves F♯–D♯ melody notes against a I (D chord). A point of interest is the raised A melody note against a D/F♯ chord on "name", "three" and "name". A significant moment is the substitution of a ♯iv^o chord (G♯dim) for the more standard II⁷ as part of the progression to V⁷ (A⁷ chord on "You know my name") and I (D chord after "number") that closes the verse. The song is also notable for use of the 5th chord tone on the VII chord to produce extra dissonance.

...
Wikipedia