The CAS Registry Mumber 33918-09-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 3,3,9,1 and 8 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 33918-09: (7*3)+(6*3)+(5*9)+(4*1)+(3*8)+(2*0)+(1*9)=121 121 % 10 = 1 So 33918-09-1 is a valid CAS Registry Number.