The CAS Registry Mumber 185304-90-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,8,5,3,0 and 4 respectively; the second part has 2 digits, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 185304-90: (8*1)+(7*8)+(6*5)+(5*3)+(4*0)+(3*4)+(2*9)+(1*0)=139 139 % 10 = 9 So 185304-90-9 is a valid CAS Registry Number.