what is the command to find out how many duplicate entries you have in 1 column, then also make excel list the names of those duplicate entries.

for example: say column a contains the following numbers:
219
457
219
345
789
10
345
345

I want column B to say that 219 and 345 were duplicated in column a, and also count how many times they have been duplicated, "2" for 219 and "3" for 345.