The CAS Registry Mumber 2615-55-6 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,6,1 and 5 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 2615-55: (6*2)+(5*6)+(4*1)+(3*5)+(2*5)+(1*5)=76 76 % 10 = 6 So 2615-55-6 is a valid CAS Registry Number.