The CAS Registry Mumber 128442-09-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,4,4 and 2 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 128442-09: (8*1)+(7*2)+(6*8)+(5*4)+(4*4)+(3*2)+(2*0)+(1*9)=121 121 % 10 = 1 So 128442-09-1 is a valid CAS Registry Number.