Formula to generate unique list in same sequence as original

[kev_]

BACKGROUND (in case it helps)
I asked a similar question on another thread - remove immediately sequential duplicated values

In that thread, numbers were allowed to appear more than once in column C but not in immediately adjacent rows
One of the solutions provided used AGGREGATE to avoid requirement to confirm with {CTRL}{SHIFT}{ENTER}
In B2
=IFERROR(INDEX(A:A,AGGREGATE(15,6,ROW($A$2:$A$21)/($A$2:$A$21<>$A$1:$A$20),ROWS(B$2:B2))),"")

THIS REQUEST (see image below)
Each value can appear only ONCE in column C and must be in the same sequence as the first occurrence in column A

I can get the numbers I want with this formula in column B
=IF(COUNTIF($A$2:A2,A2)=1,A2,"")

But I do not want any blank cells in between the values

I will be grateful for any solution, but is there is as a way to modify the above formula and thus avoid {CTRL}{SHIFT}{ENTER} ?
There are no blank cells in column A
The cells contain postitive integers < 1000

Many thanks

RemoveDuplicates.jpg

[PaulM100]

Like this? =IFERROR(INDEX($A$2:$A$21,MATCH(0,INDEX(COUNTIF($C$1:C1,$A$2:$A$21),0,0),0)),"")

[kev_]

Like this?

Just like that!
Thank you

[PaulM100]

No worries, glad to help