The CAS Registry Mumber 211797-77-2 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,1,1,7,9 and 7 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 211797-77: (8*2)+(7*1)+(6*1)+(5*7)+(4*9)+(3*7)+(2*7)+(1*7)=142 142 % 10 = 2 So 211797-77-2 is a valid CAS Registry Number.