The CAS Registry Mumber 5056-56-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,0,5 and 6 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 5056-56: (6*5)+(5*0)+(4*5)+(3*6)+(2*5)+(1*6)=84 84 % 10 = 4 So 5056-56-4 is a valid CAS Registry Number.