The CAS Registry Mumber 121177-79-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,1,1,7 and 7 respectively; the second part has 2 digits, 7 and 9 respectively. Calculate Digit Verification of CAS Registry Number 121177-79: (8*1)+(7*2)+(6*1)+(5*1)+(4*7)+(3*7)+(2*7)+(1*9)=105 105 % 10 = 5 So 121177-79-5 is a valid CAS Registry Number.