The CAS Registry Mumber 105051-53-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,5,0,5 and 1 respectively; the second part has 2 digits, 5 and 3 respectively. Calculate Digit Verification of CAS Registry Number 105051-53: (8*1)+(7*0)+(6*5)+(5*0)+(4*5)+(3*1)+(2*5)+(1*3)=74 74 % 10 = 4 So 105051-53-4 is a valid CAS Registry Number.