The CAS Registry Mumber 5583-56-2 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,5,8 and 3 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 5583-56: (6*5)+(5*5)+(4*8)+(3*3)+(2*5)+(1*6)=112 112 % 10 = 2 So 5583-56-2 is a valid CAS Registry Number.