User blog comment:Simplicityaboveall/Insanely Fast-Growing Functions/@comment-28606698-20170922185938/@comment-28606698-20170922191650

$$h_{90}(10)\approx 10\rightarrow10\rightarrow10\rightarrow91$$

$$f_{\omega^2}(10)\approx \underbrace{10\rightarrow10\cdots\rightarrow10\rightarrow10}_{12 \quad tens}$$