The CAS Registry Mumber 17659-13-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,7,6,5 and 9 respectively; the second part has 2 digits, 1 and 3 respectively. Calculate Digit Verification of CAS Registry Number 17659-13: (7*1)+(6*7)+(5*6)+(4*5)+(3*9)+(2*1)+(1*3)=131 131 % 10 = 1 So 17659-13-1 is a valid CAS Registry Number.