A sequence often used at the start of rock songs. It has several variants including "A 1 A 2, A 1-2-3-4!"

However it sounds a litle stupid in the middle of songs (see Altogether Now by the Beatles).

ALso the first 4 numbers!

This is a term associated with rock music, notably punk rock as this is what a given band member would yell out right before starting a song at a concert. It was made famous by the New York punk rock band The Ramones, whose bassist Dee Dee Ramone would always yell out before every song
and sometimes even during them.