The CAS Registry Mumber 77741-88-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,7,7,4 and 1 respectively; the second part has 2 digits, 8 and 8 respectively. Calculate Digit Verification of CAS Registry Number 77741-88: (7*7)+(6*7)+(5*7)+(4*4)+(3*1)+(2*8)+(1*8)=169 169 % 10 = 9 So 77741-88-9 is a valid CAS Registry Number.