The CAS Registry Mumber 78841-26-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,8,4 and 1 respectively; the second part has 2 digits, 2 and 6 respectively. Calculate Digit Verification of CAS Registry Number 78841-26: (7*7)+(6*8)+(5*8)+(4*4)+(3*1)+(2*2)+(1*6)=166 166 % 10 = 6 So 78841-26-6 is a valid CAS Registry Number.