In MS Excel, how do I fill in a column with the same cell from sequential
worksheet tabs automatically

For example I want my column of cells to automatically copy the same cell
$H$6 from all the sequential worksheets 1-20

so for the first cell in the column I have: ='1'!$H$6
But how do I get the cell below it in this column to increment to: ='2'!$H$6
when I do a copy and fill? the " ='1' " part doesn't seem to want to
increment, even if I try " ='+1' "

Thx,
Curt