The CAS Registry Mumber 54855-18-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,4,8,5 and 5 respectively; the second part has 2 digits, 1 and 8 respectively. Calculate Digit Verification of CAS Registry Number 54855-18: (7*5)+(6*4)+(5*8)+(4*5)+(3*5)+(2*1)+(1*8)=144 144 % 10 = 4 So 54855-18-4 is a valid CAS Registry Number.