The CAS Registry Mumber 72687-33-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,2,6,8 and 7 respectively; the second part has 2 digits, 3 and 3 respectively. Calculate Digit Verification of CAS Registry Number 72687-33: (7*7)+(6*2)+(5*6)+(4*8)+(3*7)+(2*3)+(1*3)=153 153 % 10 = 3 So 72687-33-3 is a valid CAS Registry Number.