The CAS Registry Mumber 23667-36-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,3,6,6 and 7 respectively; the second part has 2 digits, 3 and 6 respectively. Calculate Digit Verification of CAS Registry Number 23667-36: (7*2)+(6*3)+(5*6)+(4*6)+(3*7)+(2*3)+(1*6)=119 119 % 10 = 9 So 23667-36-9 is a valid CAS Registry Number.