Try a table like this one:

A1 =RANDBETWEEN(100000,200000)
B1 =CHAR(64+ROUNDUP(RAND()*26,0))
C1 same as B1
D1 =ROUNDDOWN(RAND()*7,0)
E1 =RANDBETWEEN(D1,6)
F1 =LEFT(A1,D1)&B1&MID(A1,D1+1,E1-D1)&C1&RIGHT(A1,6-E1)

A2 =A1+ROUNDUP(RAND()*50,0)

Copy everything down across 24,000 rows. Next, select column F, copy your selection and paste as values into an empty column.

The values in column A are always unique because the roundup function makes sure you add at least one. The letters are just random. Based on the values in columns D and E, they are inserted into the number at random locations.