What is the missing number in the pattern ##1, 3, 9,## __ ##, 81##?

Same thing as others wrote but written slightly differently.

The missing number is 27

It is a matter of spotting the relationship if you can. If not obvious you will need to experiment to find what type of sequence it is; geometric or arithmetic.

Observe that there is a connection of 3 in the numbers 1,3,9 in that

##1xx3=3##

Lets experiment with that for a moment!

If we apply the same rule to 3 what will we get?

##3xx3=9## which is correct.

Ok. lets apply the same rule yet again!

##9xx3=27##

Using 27, if we apply the rule once more and get 81 we have found the correct 'rule' for this sequence.

##27xx3=81## '~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This works so the missing number is 27