The CAS Registry Mumber 17387-32-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,7,3,8 and 7 respectively; the second part has 2 digits, 3 and 2 respectively. Calculate Digit Verification of CAS Registry Number 17387-32: (7*1)+(6*7)+(5*3)+(4*8)+(3*7)+(2*3)+(1*2)=125 125 % 10 = 5 So 17387-32-5 is a valid CAS Registry Number.