data/problems/237.yml
---
:id: 237
:name: Tours on a 4 x n playing board
:url: https://projecteuler.net/problem=237
:content: |+
Let T(_n_) be the number of tours over a 4 × _n_ playing board such that:
- The tour starts in the top left corner.
- The tour consists of moves that are up, down, left, or right one square.
- The tour visits each square exactly once.
- The tour ends in the bottom left corner.
The diagram shows one tour over a 4 × 10 board:
T(10) is 2329. What is T(10<sup>12</sup>) modulo 10<sup>8</sup>?