The CAS Registry Mumber 1788-56-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,7,8 and 8 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 1788-56: (6*1)+(5*7)+(4*8)+(3*8)+(2*5)+(1*6)=113 113 % 10 = 3 So 1788-56-3 is a valid CAS Registry Number.