[tex]a = ( {2}^{40} + {2}^{39} + {2}^{38} ) \div 7[/tex]
[tex]a = [ {2}^{38} ( {2}^{2} + 2 + 1)] \div 7[/tex]
[tex] a =[ {2}^{38}(4 + 2 + 1) ] \div 7[/tex]
[tex]a = ( {2}^{38} \times 7) \div 7[/tex]
[tex]a = {2}^{38} \times (7 \div 7)[/tex]
[tex]a = {2}^{38} \times 1[/tex]
[tex]a = {2}^{38} [/tex]
[tex]a = {2}^{19 \times 2} [/tex]
[tex]a = { ({2}^{19} )}^{2} = > p.p[/tex]
