The CAS Registry Mumber 102131-26-0 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, 2 and 6 respectively. Calculate Digit Verification of CAS Registry Number 102131-26: (8*1)+(7*0)+(6*2)+(5*1)+(4*3)+(3*1)+(2*2)+(1*6)=50 50 % 10 = 0 So 102131-26-0 is a valid CAS Registry Number.