## A rectangular tiling

### Problem 405

Published on Sunday, 9th December 2012, 04:00 am; Solved by 363; Difficulty rating: 40%
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}) mod 17^{7} = 126897180.

Find `f`(10^{k}) for `k` = 10^{18}, give your answer modulo 17^{7}.