The CAS Registry Mumber 105395-23-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,5,3,9 and 5 respectively; the second part has 2 digits, 2 and 3 respectively. Calculate Digit Verification of CAS Registry Number 105395-23: (8*1)+(7*0)+(6*5)+(5*3)+(4*9)+(3*5)+(2*2)+(1*3)=111 111 % 10 = 1 So 105395-23-1 is a valid CAS Registry Number.