Ackermann function
In 1928, Wilhelm Ackermann defined a 3-argument function formula_18 which gradually evolved into a 2-argument function known as the Ackermann function. The "original" Ackermann function formula_21 was less similar to modern hyperoperations, because his initial conditions start with formula_30 for all "n" &gt; 2. Also he assigned addition to "n" = 0, multiplication to "n" = 1 and exponentiation to "n" = 2, so the initial conditions produce very different operations for tetration and beyond.