The CAS Registry Mumber 105351-66-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,5,3,5 and 1 respectively; the second part has 2 digits, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 105351-66: (8*1)+(7*0)+(6*5)+(5*3)+(4*5)+(3*1)+(2*6)+(1*6)=94 94 % 10 = 4 So 105351-66-4 is a valid CAS Registry Number.