S = 1 + 3 + 32 + .......... + 32008 + 32009
= ( 1 + 3 ) + ( 32 + 33 ) + ............. + ( 32008 + 32009 )
= 4 + 32( 1 + 3 ) + ............ + 32008( 1 + 3 )
= 4 + 4 . 32 + .......... + 4 . 32008
= 4( 1 + 32 +......... + 32008 ) chia hết cho 4
KL:......