The CAS Registry Mumber 289901-91-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,8,9,9,0 and 1 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 289901-91: (8*2)+(7*8)+(6*9)+(5*9)+(4*0)+(3*1)+(2*9)+(1*1)=193 193 % 10 = 3 So 289901-91-3 is a valid CAS Registry Number.