The CAS Registry Mumber 41726-56-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 4,1,7,2 and 6 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 41726-56: (7*4)+(6*1)+(5*7)+(4*2)+(3*6)+(2*5)+(1*6)=111 111 % 10 = 1 So 41726-56-1 is a valid CAS Registry Number.