The CAS Registry Mumber 23356-34-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,3,3,5 and 6 respectively; the second part has 2 digits, 3 and 4 respectively. Calculate Digit Verification of CAS Registry Number 23356-34: (7*2)+(6*3)+(5*3)+(4*5)+(3*6)+(2*3)+(1*4)=95 95 % 10 = 5 So 23356-34-5 is a valid CAS Registry Number.