The CAS Registry Mumber 158419-81-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,8,4,1 and 9 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 158419-81: (8*1)+(7*5)+(6*8)+(5*4)+(4*1)+(3*9)+(2*8)+(1*1)=159 159 % 10 = 9 So 158419-81-9 is a valid CAS Registry Number.