The CAS Registry Mumber 163632-55-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,6,3,6,3 and 2 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 163632-55: (8*1)+(7*6)+(6*3)+(5*6)+(4*3)+(3*2)+(2*5)+(1*5)=131 131 % 10 = 1 So 163632-55-1 is a valid CAS Registry Number.