Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

greatest common divisor

The largest positive integer dividing both of two given integers, written $\gcd(a,b)$ .

Examples

$\gcd(12,18)=6$ .