---
id: 5900f5021000cf542c510014
title: 'Problem 405: A rectangular tiling'
challengeType: 5
forumTopicId: 302073
dashedName: problem-405-a-rectangular-tiling
---
# --description--
We wish to tile a rectangle whose length is twice its width.
Let $T(0)$ be the tiling consisting of a single rectangle.
For $n > 0$, let $T(n)$ be obtained from $T( n- 1)$ by replacing all tiles in the following manner:
The following animation demonstrates the tilings $T(n)$ for $n$ from 0 to 5:
Let $f(n)$ be the number of points where four tiles meet in $T(n)$. For example, $f(1) = 0$, $f(4) = 82$ and $f({10}^9)\bmod {17}^7 = 126\\,897\\,180$.
Find $f({10}^k)$ for $k = {10}^{18}$, give your answer modulo ${17}^7$.
# --hints--
`rectangularTiling()` should return `237696125`.
```js
assert.strictEqual(rectangularTiling(), 237696125);
```
# --seed--
## --seed-contents--
```js
function rectangularTiling() {
return true;
}
rectangularTiling();
```
# --solutions--
```js
// solution required
```