one method
use a helper column
if your data is in column A
in B1 enter
=countif(A:A,A1)
copy and paste down as far as you need
anything greater than 1 will have a duplicate

"MRDAPkelley" wrote:

I have a spreadsheet with several hundred 17 digit alphanumeric numbers in a
column. Is there a way that the spreadsheet can find and identify all the
duplicate numbers without my having to read each of them to find them
visually ?

Example:
4A3AK34T06E052600
4A3AK34T86E051890
4A3AK24F07E001863
4A3AK24F26E060024
4A3AK24F36E059996
4A3AK24F56E058610
4A3AK24F87E002002
4A3AK24F87E002002
4A3AK24F96E057539
4A3AK24F07E004830
4A3AK24F27E004778
4A3AK24F77E003867
4A3AK24FX7E004916
4A3AL25F87E005297
4A3AK34T67E007355
4A3AL25F47E006687
4A3AL35T07E005791
4A3AK24F17E010992
4A3AK24F87E009922
4A3AK24FX7E008223
4A3AK34T77E008336
4A3AL35T37E008426
4A3AL35T87E008518
4A3AL35T87E008518
4A3AK24F47E014275
4A3AK24F27E018597
4A3AK24F27E019300