The CAS Registry Mumber 20972-44-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,0,9,7 and 2 respectively; the second part has 2 digits, 4 and 4 respectively. Calculate Digit Verification of CAS Registry Number 20972-44: (7*2)+(6*0)+(5*9)+(4*7)+(3*2)+(2*4)+(1*4)=105 105 % 10 = 5 So 20972-44-5 is a valid CAS Registry Number.