The CAS Registry Mumber 225506-81-0 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,2,5,5,0 and 6 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 225506-81: (8*2)+(7*2)+(6*5)+(5*5)+(4*0)+(3*6)+(2*8)+(1*1)=120 120 % 10 = 0 So 225506-81-0 is a valid CAS Registry Number.