The CAS Registry Mumber 109858-77-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,9,8,5 and 8 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 109858-77: (8*1)+(7*0)+(6*9)+(5*8)+(4*5)+(3*8)+(2*7)+(1*7)=167 167 % 10 = 7 So 109858-77-7 is a valid CAS Registry Number.