The CAS Registry Mumber 56519-16-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,6,5,1 and 9 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 56519-16: (7*5)+(6*6)+(5*5)+(4*1)+(3*9)+(2*1)+(1*6)=135 135 % 10 = 5 So 56519-16-5 is a valid CAS Registry Number.