[tex]{23}^{5} + {23}^{12}+ {23}^{2003} \equiv (-1)^{5} + (-1)^{12}+ (-1)^{2003} \equiv -1+1-1 \equiv 3[/tex]
-> [tex]{23}^{5} + {23}^{12}+ {23}^{2003}=4k+3[/tex] -> [tex]{23}^{5} + {23}^{12}+ {23}^{2003}[/tex] chia 4 dư 3 mà ko có SCP nào chia 4 dư 3 -> [tex]{23}^{5} + {23}^{12}+ {23}^{2003}[/tex] ko là SCP