Do you mean 9² = 81 ? Coz eighty-one 9s multiplied together is a really big number. Like what most answerers said, it's close to 200 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
or about 2 x 10^77.
9^81= 9x9x9---------x9 81 times
Let x=9^81
log x= log 9^81= 81 log 9
Find the value of log 9 from logritmic table and multiply by 81.
Now taking antilog of this number you will get the value of 9^81