The CAS Registry Mumber 65731-67-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 6,5,7,3 and 1 respectively; the second part has 2 digits, 6 and 7 respectively. Calculate Digit Verification of CAS Registry Number 65731-67: (7*6)+(6*5)+(5*7)+(4*3)+(3*1)+(2*6)+(1*7)=141 141 % 10 = 1 So 65731-67-1 is a valid CAS Registry Number.