The CAS Registry Mumber 729-51-1 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 7,2 and 9 respectively; the second part has 2 digits, 5 and 1 respectively. Calculate Digit Verification of CAS Registry Number 729-51: (5*7)+(4*2)+(3*9)+(2*5)+(1*1)=81 81 % 10 = 1 So 729-51-1 is a valid CAS Registry Number.