The CAS Registry Mumber 219701-42-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,1,9,7,0 and 1 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 219701-42: (8*2)+(7*1)+(6*9)+(5*7)+(4*0)+(3*1)+(2*4)+(1*2)=125 125 % 10 = 5 So 219701-42-5 is a valid CAS Registry Number.