The CAS Registry Mumber 4905-26-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 4,9,0 and 5 respectively; the second part has 2 digits, 2 and 6 respectively. Calculate Digit Verification of CAS Registry Number 4905-26: (6*4)+(5*9)+(4*0)+(3*5)+(2*2)+(1*6)=94 94 % 10 = 4 So 4905-26-4 is a valid CAS Registry Number.