The CAS Registry Mumber 86691-97-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,6,6,9 and 1 respectively; the second part has 2 digits, 9 and 7 respectively. Calculate Digit Verification of CAS Registry Number 86691-97: (7*8)+(6*6)+(5*6)+(4*9)+(3*1)+(2*9)+(1*7)=186 186 % 10 = 6 So 86691-97-6 is a valid CAS Registry Number.