The CAS Registry Mumber 28805-15-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,8,8,0 and 5 respectively; the second part has 2 digits, 1 and 5 respectively. Calculate Digit Verification of CAS Registry Number 28805-15: (7*2)+(6*8)+(5*8)+(4*0)+(3*5)+(2*1)+(1*5)=124 124 % 10 = 4 So 28805-15-4 is a valid CAS Registry Number.