The CAS Registry Mumber 73717-77-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,3,7,1 and 7 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 73717-77: (7*7)+(6*3)+(5*7)+(4*1)+(3*7)+(2*7)+(1*7)=148 148 % 10 = 8 So 73717-77-8 is a valid CAS Registry Number.