The CAS Registry Mumber 1905-06-2 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,9,0 and 5 respectively; the second part has 2 digits, 0 and 6 respectively. Calculate Digit Verification of CAS Registry Number 1905-06: (6*1)+(5*9)+(4*0)+(3*5)+(2*0)+(1*6)=72 72 % 10 = 2 So 1905-06-2 is a valid CAS Registry Number.