The CAS Registry Mumber 105202-57-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,5,2,0 and 2 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 105202-57: (8*1)+(7*0)+(6*5)+(5*2)+(4*0)+(3*2)+(2*5)+(1*7)=71 71 % 10 = 1 So 105202-57-1 is a valid CAS Registry Number.