The CAS Registry Mumber 13043-77-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,3,0,4 and 3 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 13043-77: (7*1)+(6*3)+(5*0)+(4*4)+(3*3)+(2*7)+(1*7)=71 71 % 10 = 1 So 13043-77-1 is a valid CAS Registry Number.