The CAS Registry Mumber 17618-65-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,7,6,1 and 8 respectively; the second part has 2 digits, 6 and 5 respectively. Calculate Digit Verification of CAS Registry Number 17618-65: (7*1)+(6*7)+(5*6)+(4*1)+(3*8)+(2*6)+(1*5)=124 124 % 10 = 4 So 17618-65-4 is a valid CAS Registry Number.