The CAS Registry Mumber 1391999-42-0 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 2 respectively. Calculate Digit Verification of CAS Registry Number 1391999-42: (9*1)+(8*3)+(7*9)+(6*1)+(5*9)+(4*9)+(3*9)+(2*4)+(1*2)=220 220 % 10 = 0 So 1391999-42-0 is a valid CAS Registry Number.