The CAS Registry Mumber 218797-17-2 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,1,8,7,9 and 7 respectively; the second part has 2 digits, 1 and 7 respectively. Calculate Digit Verification of CAS Registry Number 218797-17: (8*2)+(7*1)+(6*8)+(5*7)+(4*9)+(3*7)+(2*1)+(1*7)=172 172 % 10 = 2 So 218797-17-2 is a valid CAS Registry Number.