The CAS Registry Mumber 303174-81-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 3,0,3,1,7 and 4 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 303174-81: (8*3)+(7*0)+(6*3)+(5*1)+(4*7)+(3*4)+(2*8)+(1*1)=104 104 % 10 = 4 So 303174-81-4 is a valid CAS Registry Number.