The CAS Registry Mumber 21164-15-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,1,1,6 and 4 respectively; the second part has 2 digits, 1 and 5 respectively. Calculate Digit Verification of CAS Registry Number 21164-15: (7*2)+(6*1)+(5*1)+(4*6)+(3*4)+(2*1)+(1*5)=68 68 % 10 = 8 So 21164-15-8 is a valid CAS Registry Number.