The CAS Registry Mumber 83724-66-7 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, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 83724-66: (7*8)+(6*3)+(5*7)+(4*2)+(3*4)+(2*6)+(1*6)=147 147 % 10 = 7 So 83724-66-7 is a valid CAS Registry Number.