The CAS Registry Mumber 155997-19-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,5,9,9 and 7 respectively; the second part has 2 digits, 1 and 9 respectively. Calculate Digit Verification of CAS Registry Number 155997-19: (8*1)+(7*5)+(6*5)+(5*9)+(4*9)+(3*7)+(2*1)+(1*9)=186 186 % 10 = 6 So 155997-19-6 is a valid CAS Registry Number.