The CAS Registry Mumber 6500-31-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 6,5,0 and 0 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 6500-31: (6*6)+(5*5)+(4*0)+(3*0)+(2*3)+(1*1)=68 68 % 10 = 8 So 6500-31-8 is a valid CAS Registry Number.