The CAS Registry Mumber 84009-56-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,4,0,0 and 9 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 84009-56: (7*8)+(6*4)+(5*0)+(4*0)+(3*9)+(2*5)+(1*6)=123 123 % 10 = 3 So 84009-56-3 is a valid CAS Registry Number.