The CAS Registry Mumber 167817-58-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,6,7,8,1 and 7 respectively; the second part has 2 digits, 5 and 8 respectively. Calculate Digit Verification of CAS Registry Number 167817-58: (8*1)+(7*6)+(6*7)+(5*8)+(4*1)+(3*7)+(2*5)+(1*8)=175 175 % 10 = 5 So 167817-58-5 is a valid CAS Registry Number.