The CAS Registry Mumber 218598-90-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,1,8,5,9 and 8 respectively; the second part has 2 digits, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 218598-90: (8*2)+(7*1)+(6*8)+(5*5)+(4*9)+(3*8)+(2*9)+(1*0)=174 174 % 10 = 4 So 218598-90-4 is a valid CAS Registry Number.