The CAS Registry Mumber 51905-97-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,1,9,0 and 5 respectively; the second part has 2 digits, 9 and 7 respectively. Calculate Digit Verification of CAS Registry Number 51905-97: (7*5)+(6*1)+(5*9)+(4*0)+(3*5)+(2*9)+(1*7)=126 126 % 10 = 6 So 51905-97-6 is a valid CAS Registry Number.