# Does a cofactor of an elliptic curve have to be an integer?

What are the implications of a curve having a non-integer co-factor for its generator point? Is that even possible?

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It depends on what you mean by "non-integer". If you have a rational like $\frac{2}{3}$, then that's possible ( if the inverse element exist, that's just a hidden inteder, because $3^{-1}$ is not a fraction but another integer). If you have a irrational number, then no. –  tylo Feb 18 '14 at 10:53
tylo, very good point. I'd give you an upvote if you made an answer. –  samoz Feb 24 '14 at 2:54