The CAS Registry Mumber 156593-80-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,6,5,9 and 3 respectively; the second part has 2 digits, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 156593-80: (8*1)+(7*5)+(6*6)+(5*5)+(4*9)+(3*3)+(2*8)+(1*0)=165 165 % 10 = 5 So 156593-80-5 is a valid CAS Registry Number.