The CAS Registry Mumber 136612-56-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,6,6,1 and 2 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 136612-56: (8*1)+(7*3)+(6*6)+(5*6)+(4*1)+(3*2)+(2*5)+(1*6)=121 121 % 10 = 1 So 136612-56-1 is a valid CAS Registry Number.