The CAS Registry Mumber 1831-56-7 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,8,3 and 1 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 1831-56: (6*1)+(5*8)+(4*3)+(3*1)+(2*5)+(1*6)=77 77 % 10 = 7 So 1831-56-7 is a valid CAS Registry Number.