The CAS Registry Mumber 252949-42-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,5,2,9,4 and 9 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 252949-42: (8*2)+(7*5)+(6*2)+(5*9)+(4*4)+(3*9)+(2*4)+(1*2)=161 161 % 10 = 1 So 252949-42-1 is a valid CAS Registry Number.