The CAS Registry Mumber 1778-71-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,7,7 and 8 respectively; the second part has 2 digits, 7 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1778-71: (6*1)+(5*7)+(4*7)+(3*8)+(2*7)+(1*1)=108 108 % 10 = 8 So 1778-71-8 is a valid CAS Registry Number.