The CAS Registry Mumber 263902-83-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,6,3,9,0 and 2 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 263902-83: (8*2)+(7*6)+(6*3)+(5*9)+(4*0)+(3*2)+(2*8)+(1*3)=146 146 % 10 = 6 So 263902-83-6 is a valid CAS Registry Number.