The CAS Registry Mumber 51907-86-9 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 7 respectively; the second part has 2 digits, 8 and 6 respectively. Calculate Digit Verification of CAS Registry Number 51907-86: (7*5)+(6*1)+(5*9)+(4*0)+(3*7)+(2*8)+(1*6)=129 129 % 10 = 9 So 51907-86-9 is a valid CAS Registry Number.