The CAS Registry Mumber 102131-35-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,2,1,3 and 1 respectively; the second part has 2 digits, 3 and 5 respectively. Calculate Digit Verification of CAS Registry Number 102131-35: (8*1)+(7*0)+(6*2)+(5*1)+(4*3)+(3*1)+(2*3)+(1*5)=51 51 % 10 = 1 So 102131-35-1 is a valid CAS Registry Number.