The CAS Registry Mumber 635731-83-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 6,3,5,7,3 and 1 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 635731-83: (8*6)+(7*3)+(6*5)+(5*7)+(4*3)+(3*1)+(2*8)+(1*3)=168 168 % 10 = 8 So 635731-83-8 is a valid CAS Registry Number.