The CAS Registry Mumber 7734-61-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,7,3 and 4 respectively; the second part has 2 digits, 6 and 1 respectively. Calculate Digit Verification of CAS Registry Number 7734-61: (6*7)+(5*7)+(4*3)+(3*4)+(2*6)+(1*1)=114 114 % 10 = 4 So 7734-61-4 is a valid CAS Registry Number.