The CAS Registry Mumber 81209-86-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,1,2,0 and 9 respectively; the second part has 2 digits, 8 and 6 respectively. Calculate Digit Verification of CAS Registry Number 81209-86: (7*8)+(6*1)+(5*2)+(4*0)+(3*9)+(2*8)+(1*6)=121 121 % 10 = 1 So 81209-86-1 is a valid CAS Registry Number.