The CAS Registry Mumber 19503-17-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,9,5,0 and 3 respectively; the second part has 2 digits, 1 and 7 respectively. Calculate Digit Verification of CAS Registry Number 19503-17: (7*1)+(6*9)+(5*5)+(4*0)+(3*3)+(2*1)+(1*7)=104 104 % 10 = 4 So 19503-17-4 is a valid CAS Registry Number.