The CAS Registry Mumber 105158-38-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,5,1,5 and 8 respectively; the second part has 2 digits, 3 and 8 respectively. Calculate Digit Verification of CAS Registry Number 105158-38: (8*1)+(7*0)+(6*5)+(5*1)+(4*5)+(3*8)+(2*3)+(1*8)=101 101 % 10 = 1 So 105158-38-1 is a valid CAS Registry Number.