Write a general formula of the following sequence: 1, 0, - 13, 0, 15, 0, - 17, 0

Write a general formula of the following sequence: 1, 0, - 13, 0, 15, 0, - 17, 0

When n is even, an = 0; when n is odd, if n = 4K + 1, then an = (- 1) n + 1 · 1n; if n = 4K + 3, then an = (- 1) n · 1n (K ∈ n)