The CAS Registry Mumber 107638-33-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,7,6,3 and 8 respectively; the second part has 2 digits, 3 and 3 respectively. Calculate Digit Verification of CAS Registry Number 107638-33: (8*1)+(7*0)+(6*7)+(5*6)+(4*3)+(3*8)+(2*3)+(1*3)=125 125 % 10 = 5 So 107638-33-5 is a valid CAS Registry Number.