The CAS Registry Mumber 4551-09-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 4,5,5 and 1 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 4551-09: (6*4)+(5*5)+(4*5)+(3*1)+(2*0)+(1*9)=81 81 % 10 = 1 So 4551-09-1 is a valid CAS Registry Number.