The CAS Registry Mumber 1391999-40-8 includes 10 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 7 digits, 1,3,9,1,9,9 and 9 respectively; the second part has 2 digits, 4 and 0 respectively. Calculate Digit Verification of CAS Registry Number 1391999-40: (9*1)+(8*3)+(7*9)+(6*1)+(5*9)+(4*9)+(3*9)+(2*4)+(1*0)=218 218 % 10 = 8 So 1391999-40-8 is a valid CAS Registry Number.