The CAS Registry Mumber 65671-24-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 6,5,6,7 and 1 respectively; the second part has 2 digits, 2 and 4 respectively. Calculate Digit Verification of CAS Registry Number 65671-24: (7*6)+(6*5)+(5*6)+(4*7)+(3*1)+(2*2)+(1*4)=141 141 % 10 = 1 So 65671-24-1 is a valid CAS Registry Number.