The CAS Registry Mumber 6623-36-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 6,6,2 and 3 respectively; the second part has 2 digits, 3 and 6 respectively. Calculate Digit Verification of CAS Registry Number 6623-36: (6*6)+(5*6)+(4*2)+(3*3)+(2*3)+(1*6)=95 95 % 10 = 5 So 6623-36-5 is a valid CAS Registry Number.