The CAS Registry Mumber 135560-59-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,5,5,6 and 0 respectively; the second part has 2 digits, 5 and 9 respectively. Calculate Digit Verification of CAS Registry Number 135560-59: (8*1)+(7*3)+(6*5)+(5*5)+(4*6)+(3*0)+(2*5)+(1*9)=127 127 % 10 = 7 So 135560-59-7 is a valid CAS Registry Number.