Square Number

Let f(x) = largest divisor of x that is square number. a * b is square number if and only if a / f(a) == b / f(b).

// Build f
let mut f = vec![0; m + 1];
for d in (1..).take_while(|&d| d * d <= m) {
    for x in ((d * d)..=m).step_by(d * d) {
        f[x] = d * d;
    }
}

• ABC254D
• ABC342D