The Ultrafactor is equal to 100!# = 100!100 in Extensible ! Notation. The term was coined by Yabuszko.[1]

Approximations in other notations

Notation Approximation
Arrow Notation \(10\uparrow^{100}158\)
Chained Arrow Notation \(10\to158\to100 \)
BEAF \(\{10,158,100\}\)
Bird's Array Notation \(\{10,158,100\}\)
Extended Hyper-E notation \(E158\# \#100\)
Hyperfactorial Array Notation \(100!99\)
Fast-growing hierarchy \(f_{101}(100)\)
Hardy hierarchy \(H_{\omega^{101}}(100)\)
Slow-growing hierarchy \(g_{\varphi(101,0)}(100)\)


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