The CAS Registry Mumber 2001-17-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,0,0 and 1 respectively; the second part has 2 digits, 1 and 7 respectively. Calculate Digit Verification of CAS Registry Number 2001-17: (6*2)+(5*0)+(4*0)+(3*1)+(2*1)+(1*7)=24 24 % 10 = 4 So 2001-17-4 is a valid CAS Registry Number.