The CAS Registry Mumber 72553-83-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,2,5,5 and 3 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 72553-83: (7*7)+(6*2)+(5*5)+(4*5)+(3*3)+(2*8)+(1*3)=134 134 % 10 = 4 So 72553-83-4 is a valid CAS Registry Number.