The CAS Registry Mumber 223545-28-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,2,3,5,4 and 5 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 223545-28: (8*2)+(7*2)+(6*3)+(5*5)+(4*4)+(3*5)+(2*2)+(1*8)=116 116 % 10 = 6 So 223545-28-6 is a valid CAS Registry Number.