The CAS Registry Mumber 78739-65-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,7,3 and 9 respectively; the second part has 2 digits, 6 and 5 respectively. Calculate Digit Verification of CAS Registry Number 78739-65: (7*7)+(6*8)+(5*7)+(4*3)+(3*9)+(2*6)+(1*5)=188 188 % 10 = 8 So 78739-65-8 is a valid CAS Registry Number.