The CAS Registry Mumber 41551-56-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 4,1,5,5 and 1 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 41551-56: (7*4)+(6*1)+(5*5)+(4*5)+(3*1)+(2*5)+(1*6)=98 98 % 10 = 8 So 41551-56-8 is a valid CAS Registry Number.