The CAS Registry Mumber 78805-28-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,8,0 and 5 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 78805-28: (7*7)+(6*8)+(5*8)+(4*0)+(3*5)+(2*2)+(1*8)=164 164 % 10 = 4 So 78805-28-4 is a valid CAS Registry Number.