The CAS Registry Mumber 3747-33-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,7,4 and 7 respectively; the second part has 2 digits, 3 and 3 respectively. Calculate Digit Verification of CAS Registry Number 3747-33: (6*3)+(5*7)+(4*4)+(3*7)+(2*3)+(1*3)=99 99 % 10 = 9 So 3747-33-9 is a valid CAS Registry Number.