I figure out an easy way to find the corresponding column from the column number.
It is ADDRESS(row_number,column_number, ) Function.
Which column is column 20?
In cell A1, type in formula =ADDRESS(1,20)
The result is $T$1.
The answer is column T.
It can also be used to quickly determine the target column (index column) in the VLOOKUP() function with the help of COLUMN() function.
ADDRESS(1,COLUMN(the first cell of the table array)+column _index number-1)
Which column we look up in the formula VLOOKUP(D14,K14:BP21,21,0)?
In cell A1, type in formula =ADDRESS(1,COLUMN(K14)+21-1)
The result is $AE$1.
The answer is column AE