The CAS Registry Mumber 53870-26-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,3,8,7 and 0 respectively; the second part has 2 digits, 2 and 6 respectively. Calculate Digit Verification of CAS Registry Number 53870-26: (7*5)+(6*3)+(5*8)+(4*7)+(3*0)+(2*2)+(1*6)=131 131 % 10 = 1 So 53870-26-1 is a valid CAS Registry Number.