[求助]请教一道数列问题

grasses

[求助]请教一道数列问题，谢谢！

The infinite sequence a₁, a₂,…, a_n,… is such that a₁ = 2, a₂ = -3, a₃ = 5, a₄ = -1, and a_n = a_n-4 for n > 4. What is the sum of the first 97 terms of the sequence?

grasses

哦 明白了，谢谢！！！