The CAS Registry Mumber 238402-55-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,3,8,4,0 and 2 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 238402-55: (8*2)+(7*3)+(6*8)+(5*4)+(4*0)+(3*2)+(2*5)+(1*5)=126 126 % 10 = 6 So 238402-55-6 is a valid CAS Registry Number.