The CAS Registry Mumber 1517-90-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,5,1 and 7 respectively; the second part has 2 digits, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 1517-90: (6*1)+(5*5)+(4*1)+(3*7)+(2*9)+(1*0)=74 74 % 10 = 4 So 1517-90-4 is a valid CAS Registry Number.