The CAS Registry Mumber 55405-22-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,5,4,0 and 5 respectively; the second part has 2 digits, 2 and 2 respectively. Calculate Digit Verification of CAS Registry Number 55405-22: (7*5)+(6*5)+(5*4)+(4*0)+(3*5)+(2*2)+(1*2)=106 106 % 10 = 6 So 55405-22-6 is a valid CAS Registry Number.