The CAS Registry Mumber 187805-78-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,8,7,8,0 and 5 respectively; the second part has 2 digits, 7 and 8 respectively. Calculate Digit Verification of CAS Registry Number 187805-78: (8*1)+(7*8)+(6*7)+(5*8)+(4*0)+(3*5)+(2*7)+(1*8)=183 183 % 10 = 3 So 187805-78-3 is a valid CAS Registry Number.