Increment a row up with increasing number

Julydoo 

Cells from 1 to 20 can be clicked with = A1 + 1 and the cell at the bottom right and dragged down.

From 20 to 1 exactly the same, only use instead of plus minus = A1-1

I would be happy to know if I could help.

Nikolino

I know I don't know anything (Socrates)

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