The CAS Registry Mumber 3901-59-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,9,0 and 1 respectively; the second part has 2 digits, 5 and 9 respectively. Calculate Digit Verification of CAS Registry Number 3901-59: (6*3)+(5*9)+(4*0)+(3*1)+(2*5)+(1*9)=85 85 % 10 = 5 So 3901-59-5 is a valid CAS Registry Number.