title: Problem 811
date: 2022/10/08 06:00:00
---

***
# [Problem 811](https://projecteuler.net/problem=811)
***
[Xem đề gốc (tiếng Anh)](https://projecteuler.net/problem=811)

## **Truy hồi bit**

$f(0) = 0$, $f(2n) = f(n)$, $f(2n+1) = 1 - f(n)$. Tính $\sum_{n=0}^{10^{15}} f(n)$.

***