The CAS Registry Mumber 21411-08-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,1,4,1 and 1 respectively; the second part has 2 digits, 0 and 8 respectively. Calculate Digit Verification of CAS Registry Number 21411-08: (7*2)+(6*1)+(5*4)+(4*1)+(3*1)+(2*0)+(1*8)=55 55 % 10 = 5 So 21411-08-5 is a valid CAS Registry Number.