The CAS Registry Mumber 204251-23-0 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,0,4,2,5 and 1 respectively; the second part has 2 digits, 2 and 3 respectively. Calculate Digit Verification of CAS Registry Number 204251-23: (8*2)+(7*0)+(6*4)+(5*2)+(4*5)+(3*1)+(2*2)+(1*3)=80 80 % 10 = 0 So 204251-23-0 is a valid CAS Registry Number.