The CAS Registry Mumber 73-38-1 includes 5 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 2 digits, 7 and 3 respectively; the second part has 2 digits, 3 and 8 respectively. Calculate Digit Verification of CAS Registry Number 73-38: (4*7)+(3*3)+(2*3)+(1*8)=51 51 % 10 = 1 So 73-38-1 is a valid CAS Registry Number.