The CAS Registry Mumber 80304-21-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,0,3,0 and 4 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 80304-21: (7*8)+(6*0)+(5*3)+(4*0)+(3*4)+(2*2)+(1*1)=88 88 % 10 = 8 So 80304-21-8 is a valid CAS Registry Number.