The CAS Registry Mumber 263903-62-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,6,3,9,0 and 3 respectively; the second part has 2 digits, 6 and 2 respectively. Calculate Digit Verification of CAS Registry Number 263903-62: (8*2)+(7*6)+(6*3)+(5*9)+(4*0)+(3*3)+(2*6)+(1*2)=144 144 % 10 = 4 So 263903-62-4 is a valid CAS Registry Number.