The CAS Registry Mumber 26502-00-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,6,5,0 and 2 respectively; the second part has 2 digits, 0 and 0 respectively. Calculate Digit Verification of CAS Registry Number 26502-00: (7*2)+(6*6)+(5*5)+(4*0)+(3*2)+(2*0)+(1*0)=81 81 % 10 = 1 So 26502-00-1 is a valid CAS Registry Number.