The CAS Registry Mumber 1718-94-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,7,1 and 8 respectively; the second part has 2 digits, 9 and 4 respectively. Calculate Digit Verification of CAS Registry Number 1718-94: (6*1)+(5*7)+(4*1)+(3*8)+(2*9)+(1*4)=91 91 % 10 = 1 So 1718-94-1 is a valid CAS Registry Number.