The CAS Registry Mumber 18993-26-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,8,9,9 and 3 respectively; the second part has 2 digits, 2 and 6 respectively. Calculate Digit Verification of CAS Registry Number 18993-26: (7*1)+(6*8)+(5*9)+(4*9)+(3*3)+(2*2)+(1*6)=155 155 % 10 = 5 So 18993-26-5 is a valid CAS Registry Number.