The CAS Registry Mumber 82791-56-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,2,7,9 and 1 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 82791-56: (7*8)+(6*2)+(5*7)+(4*9)+(3*1)+(2*5)+(1*6)=158 158 % 10 = 8 So 82791-56-8 is a valid CAS Registry Number.