The CAS Registry Mumber 1747-42-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,7,4 and 7 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 1747-42: (6*1)+(5*7)+(4*4)+(3*7)+(2*4)+(1*2)=88 88 % 10 = 8 So 1747-42-8 is a valid CAS Registry Number.