The CAS Registry Mumber 26258-28-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,6,2,5 and 8 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 26258-28: (7*2)+(6*6)+(5*2)+(4*5)+(3*8)+(2*2)+(1*8)=116 116 % 10 = 6 So 26258-28-6 is a valid CAS Registry Number.