The CAS Registry Mumber 12651-21-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,2,6,5 and 1 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 12651-21: (7*1)+(6*2)+(5*6)+(4*5)+(3*1)+(2*2)+(1*1)=77 77 % 10 = 7 So 12651-21-7 is a valid CAS Registry Number.