The CAS Registry Mumber 736-78-7 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 7,3 and 6 respectively; the second part has 2 digits, 7 and 8 respectively. Calculate Digit Verification of CAS Registry Number 736-78: (5*7)+(4*3)+(3*6)+(2*7)+(1*8)=87 87 % 10 = 7 So 736-78-7 is a valid CAS Registry Number.