VIM replaces how to use the hit part in the pattern string

  question, vim

The description of the problem is rather obscure. I will give a direct example.
There is a file like this

A1
A2
A3

Hope to be replaced by

F1B1
F2B2
F3B3

How should it be written?

Vim’s regular expression is quite special, seehttp://vimregex.com/However, backward references are supported, but escaped brackets are required.\(And\), and then in the replacement part in order to reference (such as,\1) is ok.

:%s:A\(\d\+\):F\1B\1:g