Given:
f(x)=Sum[x/n!] for all positive integers n, where the [] brackets define the integer part of x (e.g. [pi]=3)

What is x, if f(x)=1215

(In reply to Solution by Jer)

You found f(1215). The puzzle asks, in effect, for the inverse function.

Posted by Charlie on 2023-09-25 08:44:01