The CAS Registry Mumber 4143-15-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 4,1,4 and 3 respectively; the second part has 2 digits, 1 and 5 respectively. Calculate Digit Verification of CAS Registry Number 4143-15: (6*4)+(5*1)+(4*4)+(3*3)+(2*1)+(1*5)=61 61 % 10 = 1 So 4143-15-1 is a valid CAS Registry Number.