The CAS Registry Mumber 291758-11-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,9,1,7,5 and 8 respectively; the second part has 2 digits, 1 and 1 respectively. Calculate Digit Verification of CAS Registry Number 291758-11: (8*2)+(7*9)+(6*1)+(5*7)+(4*5)+(3*8)+(2*1)+(1*1)=167 167 % 10 = 7 So 291758-11-7 is a valid CAS Registry Number.