Question

The number 1111.....1(91 times) is a

A) prime b) non prime c) even

Answer 1

b is the right answer

Answer 2

111...111(91times) can be expressed as:-

⟹19×(1091−1)⟹19×(1091−1)

⟹19(107−1)×x=1111111×x⟹19(107−1)×x=1111111×x

where x=(107)12+(107)11+⋯+1
So it's not a prime no.