User blog comment:Wythagoras/Problems for the First International Googological Olympiad/@comment-5150073-20150125192350/@comment-10429372-20150125193316

Family of Bachmann-Landau notations

It means that it is grows at a comparable rate. By placing Θ(n) in the uppermost exponent, functions like 2^(2^n*n) are also allowed, so is 2^(2^n/n)