The CAS Registry Mumber 105240-65-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,5,2,4 and 0 respectively; the second part has 2 digits, 6 and 5 respectively. Calculate Digit Verification of CAS Registry Number 105240-65: (8*1)+(7*0)+(6*5)+(5*2)+(4*4)+(3*0)+(2*6)+(1*5)=81 81 % 10 = 1 So 105240-65-1 is a valid CAS Registry Number.