The CAS Registry Mumber 2651-64-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,6,5 and 1 respectively; the second part has 2 digits, 6 and 4 respectively. Calculate Digit Verification of CAS Registry Number 2651-64: (6*2)+(5*6)+(4*5)+(3*1)+(2*6)+(1*4)=81 81 % 10 = 1 So 2651-64-1 is a valid CAS Registry Number.