The CAS Registry Mumber 135182-55-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,5,1,8 and 2 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 135182-55: (8*1)+(7*3)+(6*5)+(5*1)+(4*8)+(3*2)+(2*5)+(1*5)=117 117 % 10 = 7 So 135182-55-7 is a valid CAS Registry Number.