The CAS Registry Mumber 117835-28-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,1,7,8,3 and 5 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 117835-28: (8*1)+(7*1)+(6*7)+(5*8)+(4*3)+(3*5)+(2*2)+(1*8)=136 136 % 10 = 6 So 117835-28-6 is a valid CAS Registry Number.