The CAS Registry Mumber 1604-44-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,6,0 and 4 respectively; the second part has 2 digits, 4 and 4 respectively. Calculate Digit Verification of CAS Registry Number 1604-44: (6*1)+(5*6)+(4*0)+(3*4)+(2*4)+(1*4)=60 60 % 10 = 0 So 1604-44-0 is a valid CAS Registry Number.