The CAS Registry Mumber 78917-87-0 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,9,1 and 7 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 78917-87: (7*7)+(6*8)+(5*9)+(4*1)+(3*7)+(2*8)+(1*7)=190 190 % 10 = 0 So 78917-87-0 is a valid CAS Registry Number.