@AustinVinar, yes, you have to multiply the crop factor (1.6x) when doing the math for the hand-held rule.
Also, remember that in photography, rules are very easily broken. A shutter speeed of 1/50 should be enough normally, but if your finger jiggles the camera just as it’s taking, it could very easily create blur, even at 18mm. There’s a reason that professional landscape photographers use remote control and mirror lock-up. 🙂