(-1/3)^(2n) * 3*(2n+1) + 3^(2n-1)
=(1/3)^(2n) * 3*(2n+1) + (1/3)^(2n)*3^(2n-1)
=(1/3)^(2n) * 3*(2n)*3+ (1/3)^(2n)*3^(2n)/3
=3+1/3
=10/3