The CAS Registry Mumber 3951-45-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,9,5 and 1 respectively; the second part has 2 digits, 4 and 5 respectively. Calculate Digit Verification of CAS Registry Number 3951-45: (6*3)+(5*9)+(4*5)+(3*1)+(2*4)+(1*5)=99 99 % 10 = 9 So 3951-45-9 is a valid CAS Registry Number.