[tex]\div \quad 4,7,10,13,...,100. \\ \\a_n = a_1 + (n-1)\cdot r \\ \\ (n-1)\cdot r = a_n-a_1 \\ \\ n-1 = \dfrac{a_n-a_1}{r} \\ \\ \boxed{n = \dfrac{a_n-a_1}{r}+1} \\ \\\\ \Rightarrow n = \dfrac{100-4}{3}+1 = \dfrac{96}{3}+1 = 32+1 = \boxed{33}[/tex]
