The CAS Registry Mumber 65707-77-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 6,5,7,0 and 7 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 65707-77: (7*6)+(6*5)+(5*7)+(4*0)+(3*7)+(2*7)+(1*7)=149 149 % 10 = 9 So 65707-77-9 is a valid CAS Registry Number.