The CAS Registry Mumber 155359-99-2 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,5,3,5 and 9 respectively; the second part has 2 digits, 9 and 9 respectively. Calculate Digit Verification of CAS Registry Number 155359-99: (8*1)+(7*5)+(6*5)+(5*3)+(4*5)+(3*9)+(2*9)+(1*9)=162 162 % 10 = 2 So 155359-99-2 is a valid CAS Registry Number.