How can we formular a dynamic cell? i.e. =B2 as ="B"&"2"??

Here is what I would like to have:

A B

1 B
2 10

Setup a value 'B' in cell A1 and hope to get B2 value "10" in cell A2 -
thought that using ="A1"&2 in cell A2 will work but didn't.....

/QAtest