The CAS Registry Mumber 5663-74-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,6,6 and 3 respectively; the second part has 2 digits, 7 and 4 respectively. Calculate Digit Verification of CAS Registry Number 5663-74: (6*5)+(5*6)+(4*6)+(3*3)+(2*7)+(1*4)=111 111 % 10 = 1 So 5663-74-1 is a valid CAS Registry Number.