The CAS Registry Mumber 13781-16-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,3,7,8 and 1 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 13781-16: (7*1)+(6*3)+(5*7)+(4*8)+(3*1)+(2*1)+(1*6)=103 103 % 10 = 3 So 13781-16-3 is a valid CAS Registry Number.