The CAS Registry Mumber 355409-69-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 3,5,5,4,0 and 9 respectively; the second part has 2 digits, 6 and 9 respectively. Calculate Digit Verification of CAS Registry Number 355409-69: (8*3)+(7*5)+(6*5)+(5*4)+(4*0)+(3*9)+(2*6)+(1*9)=157 157 % 10 = 7 So 355409-69-7 is a valid CAS Registry Number.