The CAS Registry Mumber 123358-26-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,3,3,5 and 8 respectively; the second part has 2 digits, 2 and 6 respectively. Calculate Digit Verification of CAS Registry Number 123358-26: (8*1)+(7*2)+(6*3)+(5*3)+(4*5)+(3*8)+(2*2)+(1*6)=109 109 % 10 = 9 So 123358-26-9 is a valid CAS Registry Number.