The CAS Registry Mumber 271261-77-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,7,1,2,6 and 1 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 271261-77: (8*2)+(7*7)+(6*1)+(5*2)+(4*6)+(3*1)+(2*7)+(1*7)=129 129 % 10 = 9 So 271261-77-9 is a valid CAS Registry Number.