The CAS Registry Mumber 107659-56-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,7,6,5 and 9 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 107659-56: (8*1)+(7*0)+(6*7)+(5*6)+(4*5)+(3*9)+(2*5)+(1*6)=143 143 % 10 = 3 So 107659-56-3 is a valid CAS Registry Number.