The CAS Registry Mumber 159898-91-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,9,8,9 and 8 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 159898-91: (8*1)+(7*5)+(6*9)+(5*8)+(4*9)+(3*8)+(2*9)+(1*1)=216 216 % 10 = 6 So 159898-91-6 is a valid CAS Registry Number.