The CAS Registry Mumber 31970-56-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 3,1,9,7 and 0 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 31970-56: (7*3)+(6*1)+(5*9)+(4*7)+(3*0)+(2*5)+(1*6)=116 116 % 10 = 6 So 31970-56-6 is a valid CAS Registry Number.