The CAS Registry Mumber 77834-54-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,7,8,3 and 4 respectively; the second part has 2 digits, 5 and 4 respectively. Calculate Digit Verification of CAS Registry Number 77834-54: (7*7)+(6*7)+(5*8)+(4*3)+(3*4)+(2*5)+(1*4)=169 169 % 10 = 9 So 77834-54-9 is a valid CAS Registry Number.