The CAS Registry Mumber 175689-87-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,7,5,6,8 and 9 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 175689-87: (8*1)+(7*7)+(6*5)+(5*6)+(4*8)+(3*9)+(2*8)+(1*7)=199 199 % 10 = 9 So 175689-87-9 is a valid CAS Registry Number.