The CAS Registry Mumber 81880-29-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,1,8,8 and 0 respectively; the second part has 2 digits, 2 and 9 respectively. Calculate Digit Verification of CAS Registry Number 81880-29: (7*8)+(6*1)+(5*8)+(4*8)+(3*0)+(2*2)+(1*9)=147 147 % 10 = 7 So 81880-29-7 is a valid CAS Registry Number.