The CAS Registry Mumber 83724-73-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,3,7,2 and 4 respectively; the second part has 2 digits, 7 and 3 respectively. Calculate Digit Verification of CAS Registry Number 83724-73: (7*8)+(6*3)+(5*7)+(4*2)+(3*4)+(2*7)+(1*3)=146 146 % 10 = 6 So 83724-73-6 is a valid CAS Registry Number.