The CAS Registry Mumber 331815-64-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 3,3,1,8,1 and 5 respectively; the second part has 2 digits, 6 and 4 respectively. Calculate Digit Verification of CAS Registry Number 331815-64: (8*3)+(7*3)+(6*1)+(5*8)+(4*1)+(3*5)+(2*6)+(1*4)=126 126 % 10 = 6 So 331815-64-6 is a valid CAS Registry Number.