a1(0,1) ,a2(-2,0),a3(0,-3),a4(4,0),a5(0,5),a6(-6,0)
an=(n*(-1)^(n/2),0) if n is even
=(0,n*(-1)^((n-1)/2) if n is odd
n is +ve integer
a2011 = (0,-2011)
a2012 =( 2012,0)
a1(0,1) ,a2(-2,0),a3(0,-3),a4(4,0),a5(0,5),a6(-6,0)
an=(n*(-1)^(n/2),0) if n is even
=(0,n*(-1)^((n-1)/2) if n is odd
n is +ve integer
a2011 = (0,-2011)
a2012 =( 2012,0)