The CAS Registry Mumber 141991-16-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,4,1,9,9 and 1 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 141991-16: (8*1)+(7*4)+(6*1)+(5*9)+(4*9)+(3*1)+(2*1)+(1*6)=134 134 % 10 = 4 So 141991-16-4 is a valid CAS Registry Number.