The CAS Registry Mumber 128902-84-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,9,0 and 2 respectively; the second part has 2 digits, 8 and 4 respectively. Calculate Digit Verification of CAS Registry Number 128902-84: (8*1)+(7*2)+(6*8)+(5*9)+(4*0)+(3*2)+(2*8)+(1*4)=141 141 % 10 = 1 So 128902-84-1 is a valid CAS Registry Number.