The CAS Registry Mumber 77313-50-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,7,3,1 and 3 respectively; the second part has 2 digits, 5 and 0 respectively. Calculate Digit Verification of CAS Registry Number 77313-50: (7*7)+(6*7)+(5*3)+(4*1)+(3*3)+(2*5)+(1*0)=129 129 % 10 = 9 So 77313-50-9 is a valid CAS Registry Number.