The CAS Registry Mumber 1231687-28-7 includes 10 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 7 digits, 1,2,3,1,6,8 and 7 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 1231687-28: (9*1)+(8*2)+(7*3)+(6*1)+(5*6)+(4*8)+(3*7)+(2*2)+(1*8)=147 147 % 10 = 7 So 1231687-28-7 is a valid CAS Registry Number.