The CAS Registry Mumber 17817-67-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,7,8,1 and 7 respectively; the second part has 2 digits, 6 and 7 respectively. Calculate Digit Verification of CAS Registry Number 17817-67: (7*1)+(6*7)+(5*8)+(4*1)+(3*7)+(2*6)+(1*7)=133 133 % 10 = 3 So 17817-67-3 is a valid CAS Registry Number.