Add /r/dailyprogrammer Challenge #305

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+# [[2017-03-06] Challenge #305 [Easy] Permutation base](https://www.reddit.com/r/dailyprogrammer/comments/5xu7sz/20170306_challenge_305_easy_permutation_base/)
+
+There may be an actual name to this base system (let us/me know in comments),
+and there is a math insight that makes this problem even easier, but it is
+still pretty easy with no math insight.
+
+For *permutation base 2*, the indexes and values start with:
+
+| index | value |
+| :---: | ----: |
+|   0   |    0  |
+|   1   |    1  |
+|   2   |   00  |
+|   3   |   01  |
+|   4   |   10  |
+|   5   |   11  |
+|   6   |  000  |
+|   7   |  001  |
+|   8   |  010  |
+|   9   |  011  |
+
+## Sample challenge
+
+What is the base-value for index `54`?
+
+What is the index-value for base `111000111`?
+
+## Example
+
+    permbase2 54
+    1 1 0 0 0
+
+    permbase2 inv 1 1 1 0 0 0 1 1 1
+    965
+
+## Challenge index inputs (some are 64-bit+ inputs)
+
+    234234234
+    234234234234234
+    234234234234234234234234
+
+## Challenge value inputs
+
+    000111000111111000111111000111111000111
+    11111111000111000111111000111111000111111000111
+
+## Bonus
+
+Extend the function to work with any base. Base 10 index value `10` is `00`.
+Index value `109` is `99`