The Sudan function. In the theory of computation, the Sudan function is an example of a function that is recursive, but not primitive recursive. This is also true of the better-known Ackermann function. The Sudan function was the first function having this property to be published.
It was discovered (and published) in 1927 by Gabriel Sudan, a Romanian mathematician who was a student of David Hilbert.
const F = require("sudan");
console.log(F(1n, 4n, 7n)); // => 759n