The CAS Registry Mumber 56355-16-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,6,3,5 and 5 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 56355-16: (7*5)+(6*6)+(5*3)+(4*5)+(3*5)+(2*1)+(1*6)=129 129 % 10 = 9 So 56355-16-9 is a valid CAS Registry Number.