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The tethrapentaeltothol (formerly tethrapehaeltothol) is equal to E100(#^^#)^#^#^#####100 in Extended Cascading-E Notation.[1] The term was coined by Sbiis Saibian.

## Etymology

The name of this number is based on the number "tethrathoth" and the number "pentaeltothol".

## Approximations in other notations

Notation Approximation
BEAF $$\{100,100(X \uparrow\uparrow X*X^{X^{X^5}}) 2\}$$[2]
Bird's array notation $$\{100,100 [1[6]2 \backslash 2] 2\}$$
Hyperfactorial array notation $$100![1,[1,[1,[1,1,6],1,2],1,1,2],[1],1,2]$$
Fast-growing hierarchy $$f_{\varepsilon_0^{\omega^{\omega^{\omega^5}}}}(100)$$
Hardy hierarchy $$H_{\varepsilon_0^{\varepsilon_0^{\omega^{\omega^{\omega^5}}}}}(100)$$
Slow-growing hierarchy $$g_{\vartheta(\varepsilon_{\Omega 2}^{\Omega^{\Omega^{\Omega^4\omega}}})}(100)$$

## Sources

1. Saibian, Sbiis. 4.3.7 Extended Cascading-E Numbers Part IOne to Infinity. Retrieved 2015-12-09.
2. Using particular notation $$\{a,b (A) 2\} = A\ \&\ a$$ with prime b.