The CAS Registry Mumber 188966-31-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,8,8,9,6 and 6 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 188966-31: (8*1)+(7*8)+(6*8)+(5*9)+(4*6)+(3*6)+(2*3)+(1*1)=206 206 % 10 = 6 So 188966-31-6 is a valid CAS Registry Number.