The CAS Registry Mumber 20790-38-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,0,7,9 and 0 respectively; the second part has 2 digits, 3 and 8 respectively. Calculate Digit Verification of CAS Registry Number 20790-38: (7*2)+(6*0)+(5*7)+(4*9)+(3*0)+(2*3)+(1*8)=99 99 % 10 = 9 So 20790-38-9 is a valid CAS Registry Number.