Function to compute sum of the cubes with alternating sign
int summation ( int N ) { int co = ( N + 1 ) / 2 ; int ce = ( N ) / 2 ; int se = 2 * ( ( ce * ( ce + 1 ) ) * ( ce * ( ce + 1 ) ) ) ; int so = ( co * co ) * ( 2 * ( ( co * co ) ) - 1 ) ; return so - se ; }