The CAS Registry Mumber 83345-65-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,3,3,4 and 5 respectively; the second part has 2 digits, 6 and 5 respectively. Calculate Digit Verification of CAS Registry Number 83345-65: (7*8)+(6*3)+(5*3)+(4*4)+(3*5)+(2*6)+(1*5)=137 137 % 10 = 7 So 83345-65-7 is a valid CAS Registry Number.