The CAS Registry Mumber 1855-31-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,8,5 and 5 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1855-31: (6*1)+(5*8)+(4*5)+(3*5)+(2*3)+(1*1)=88 88 % 10 = 8 So 1855-31-8 is a valid CAS Registry Number.