The CAS Registry Mumber 80534-21-0 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,0,5,3 and 4 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 80534-21: (7*8)+(6*0)+(5*5)+(4*3)+(3*4)+(2*2)+(1*1)=110 110 % 10 = 0 So 80534-21-0 is a valid CAS Registry Number.