The CAS Registry Mumber 76105-56-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,6,1,0 and 5 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 76105-56: (7*7)+(6*6)+(5*1)+(4*0)+(3*5)+(2*5)+(1*6)=121 121 % 10 = 1 So 76105-56-1 is a valid CAS Registry Number.