The CAS Registry Mumber 155981-63-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,5,9,8 and 1 respectively; the second part has 2 digits, 6 and 3 respectively. Calculate Digit Verification of CAS Registry Number 155981-63: (8*1)+(7*5)+(6*5)+(5*9)+(4*8)+(3*1)+(2*6)+(1*3)=168 168 % 10 = 8 So 155981-63-8 is a valid CAS Registry Number.