Code shared from the Rust Playground

playground.rs

use std::cmp::max;
use rayon::prelude::*;

fn max_k(n: u64) -> u64 {
    let p = n as f64;
    return ((((8.0f64*p)+1.0f64).sqrt()-1.0f64)/2.0f64) as u64;
}

fn f(n: u64, k: &u64) -> u64 {
    let total = (k*(k+1))/2;
    max(1+((n-total)/k), 0)
}


fn F(n: u64) -> u64 {
    [1..max_k(n)].par_iter().map(|x| f(n, x)).sum()
}



fn main() {
    let k = f(100, &13);
    println!("{}", k);
}