The CAS Registry Mumber 142905-23-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,4,2,9,0 and 5 respectively; the second part has 2 digits, 2 and 3 respectively. Calculate Digit Verification of CAS Registry Number 142905-23: (8*1)+(7*4)+(6*2)+(5*9)+(4*0)+(3*5)+(2*2)+(1*3)=115 115 % 10 = 5 So 142905-23-5 is a valid CAS Registry Number.