The CAS Registry Mumber 85815-17-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,5,8,1 and 5 respectively; the second part has 2 digits, 1 and 7 respectively. Calculate Digit Verification of CAS Registry Number 85815-17: (7*8)+(6*5)+(5*8)+(4*1)+(3*5)+(2*1)+(1*7)=154 154 % 10 = 4 So 85815-17-4 is a valid CAS Registry Number.