The CAS Registry Mumber 13287-77-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,3,2,8 and 7 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 13287-77: (7*1)+(6*3)+(5*2)+(4*8)+(3*7)+(2*7)+(1*7)=109 109 % 10 = 9 So 13287-77-9 is a valid CAS Registry Number.