[tex]a=(7^{53}+7^{54}+7^{55}+7^{56})-(3^{27}+3^{28}+3^{29}+3^{30})[/tex]
[tex]a=7^{53}(1+7+7^{2}+7^{3})-3^{27}(1+3+3^{2}+3^{3})[/tex]
[tex]a=7^{53}(1+7+49+343)-3^{27}(1+3+9+27)[/tex]
[tex]a=7^{53}\cdot400-3^{27}\cdot40[/tex]
[tex]a=10(7^{53}\cdot40-3^{27}\cdot4)\vdots10[/tex]
[tex]-----------------[/tex]
[tex]a=7^{180}+1+4^{200}+8^{201}[/tex]
[tex]O~putere~a~unui~numar~par~este~para,~iar~o~putere~a~unui~numar~impar~este~impara[/tex]
[tex]a=impar+impar+par+par=par\vdots2[/tex]
[tex]-----------------[/tex]
[tex]9\leq x\leq49[/tex]
[tex]x\in\{9,10,11,12,\dots49\}[/tex]
