Question Number 612 by 123456 last updated on 08/Mar/15
$${encontre}\:{f}:\mathbb{N}\rightarrow\mathbb{N}\:{sobrejetivo}\:{tal}\:{que} \\ $$$${f}^{−\mathrm{1}} \left({n}\right)=\left\{{m}\mid{f}\left({m}\right)={n}\right\}\:{e}\:{infinito} \\ $$
encontre-f-N-N-sobrejetivo-tal-que-f-1-n-m-f-m-n-e-infinito-