The CAS Registry Mumber 2734-34-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,7,3 and 4 respectively; the second part has 2 digits, 3 and 4 respectively. Calculate Digit Verification of CAS Registry Number 2734-34: (6*2)+(5*7)+(4*3)+(3*4)+(2*3)+(1*4)=81 81 % 10 = 1 So 2734-34-1 is a valid CAS Registry Number.