The CAS Registry Mumber 2031-78-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,0,3 and 1 respectively; the second part has 2 digits, 7 and 8 respectively. Calculate Digit Verification of CAS Registry Number 2031-78: (6*2)+(5*0)+(4*3)+(3*1)+(2*7)+(1*8)=49 49 % 10 = 9 So 2031-78-9 is a valid CAS Registry Number.