The CAS Registry Mumber 51415-20-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,1,4,1 and 5 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 51415-20: (7*5)+(6*1)+(5*4)+(4*1)+(3*5)+(2*2)+(1*0)=84 84 % 10 = 4 So 51415-20-4 is a valid CAS Registry Number.