The CAS Registry Mumber 59121-90-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,9,1,2 and 1 respectively; the second part has 2 digits, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 59121-90: (7*5)+(6*9)+(5*1)+(4*2)+(3*1)+(2*9)+(1*0)=123 123 % 10 = 3 So 59121-90-3 is a valid CAS Registry Number.