The CAS Registry Mumber 77931-56-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,7,9,3 and 1 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 77931-56: (7*7)+(6*7)+(5*9)+(4*3)+(3*1)+(2*5)+(1*6)=167 167 % 10 = 7 So 77931-56-7 is a valid CAS Registry Number.