The CAS Registry Mumber 219701-31-2 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, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 219701-31: (8*2)+(7*1)+(6*9)+(5*7)+(4*0)+(3*1)+(2*3)+(1*1)=122 122 % 10 = 2 So 219701-31-2 is a valid CAS Registry Number.