diff --git a/2021/06/README.md b/2021/06/README.md
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+# 2021 Day 06: Lanternfish
+Copyright (c) Eric Wastl
+#### [Direct Link](https://adventofcode.com/2021/day/06)
+
+## Part 1
+
+The sea floor is getting steeper. Maybe the sleigh keys got carried this way?
+
+A massive school of glowing [lanternfish](https://en.wikipedia.org/wiki/Lanternfish) swims past. They must spawn quickly to reach such large numbers - maybe **exponentially** quickly? You should model their growth rate to be sure.
+
+Although you know nothing about this specific species of lanternfish, you make some guesses about their attributes. Surely, each lanternfish creates a new lanternfish once every **7** days.
+
+However, this process isn't necessarily synchronized between every lanternfish - one lanternfish might have 2 days left until it creates another lanternfish, while another might have 4. So, you can model each fish as a single number that represents **the number of days until it creates a new lanternfish.**
+
+Furthermore, you reason, a **new** lanternfish would surely need slightly longer before it's capable of producing more lanternfish: two more days for its first cycle.
+
+So, suppose you have a lanternfish with an internal timer value of `3`:
+
+- After one day, its internal timer would become `2`.
+- After another day, its internal timer would become `1`.
+- After another day, its internal timer would become `0`.
+- After another day, its internal timer would reset to `6`, and it would create a **new** lanternfish with an internal timer of `8`.
+- After another day, the first lanternfish would have an internal timer of `5`, and the second lanternfish would have an internal timer of `7`.
+
+A lanternfish that creates a new fish resets its timer to `6`, **not `7`** (because `0` is included as a valid timer value). The new lanternfish starts with an internal timer of `8` and does not start counting down until the next day.
+
+Realizing what you're trying to do, the submarine automatically produces a list of the ages of several hundred nearby lanternfish (your puzzle input). For example, suppose you were given the following list:
+
+```
+3,4,3,1,2
+```
+
+This list means that the first fish has an internal timer of `3`, the second fish has an internal timer of `4`, and so on until the fifth fish, which has an internal timer of `2`. Simulating these fish over several days would proceed as follows:
+
+```
+Initial state: 3,4,3,1,2
+After  1 day:  2,3,2,0,1
+After  2 days: 1,2,1,6,0,8
+After  3 days: 0,1,0,5,6,7,8
+After  4 days: 6,0,6,4,5,6,7,8,8
+After  5 days: 5,6,5,3,4,5,6,7,7,8
+After  6 days: 4,5,4,2,3,4,5,6,6,7
+After  7 days: 3,4,3,1,2,3,4,5,5,6
+After  8 days: 2,3,2,0,1,2,3,4,4,5
+After  9 days: 1,2,1,6,0,1,2,3,3,4,8
+After 10 days: 0,1,0,5,6,0,1,2,2,3,7,8
+After 11 days: 6,0,6,4,5,6,0,1,1,2,6,7,8,8,8
+After 12 days: 5,6,5,3,4,5,6,0,0,1,5,6,7,7,7,8,8
+After 13 days: 4,5,4,2,3,4,5,6,6,0,4,5,6,6,6,7,7,8,8
+After 14 days: 3,4,3,1,2,3,4,5,5,6,3,4,5,5,5,6,6,7,7,8
+After 15 days: 2,3,2,0,1,2,3,4,4,5,2,3,4,4,4,5,5,6,6,7
+After 16 days: 1,2,1,6,0,1,2,3,3,4,1,2,3,3,3,4,4,5,5,6,8
+After 17 days: 0,1,0,5,6,0,1,2,2,3,0,1,2,2,2,3,3,4,4,5,7,8
+After 18 days: 6,0,6,4,5,6,0,1,1,2,6,0,1,1,1,2,2,3,3,4,6,7,8,8,8,8
+```
+
+Each day, a `0` becomes a `6` and adds a new `8` to the end of the list, while each other number decreases by 1 if it was present at the start of the day.
+
+In this example, after 18 days, there are a total of `26` fish. After 80 days, there would be a total of **`5934`**.
+
+Find a way to simulate lanternfish. **How many lanternfish would there be after 80 days?**
+
+## Part 2
+
+Suppose the lanternfish live forever and have unlimited food and space. Would they take over the entire ocean?
+
+After 256 days in the example above, there would be a total of **`26984457539`** lanternfish!
+
+**How many lanternfish would there be after 256 days?**
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diff --git a/2021/06/code.py b/2021/06/code.py
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+++ b/2021/06/code.py
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+# SPDX-License-Identifier: MIT
+# Copyright (c) 2021 Akumatic
+#
+# https://adventofcode.com/2021/day/06
+
+def read_file(filename: str = "input.txt") -> list:
+    with open(f"{__file__.rstrip('code.py')}{filename}", "r") as f:
+        return [int(x) for x in f.read().strip().split(",")]
+
+def part1(vals: list, days: int = 80) -> int:
+    fishes = vals[:]
+    for _ in range(days):
+        for i in range(len(fishes)):
+            if fishes[i] == 0:
+                fishes[i] = 6
+                fishes.append(8)
+            else:
+                fishes[i] -= 1
+    return len(fishes)
+
+def part2(vals: list, days: int = 256) -> int:
+    fishes = [vals.count(x) for x in range(9)]
+    for _ in range(days):
+        tmp = fishes[0]
+        fishes = fishes[1:] + [tmp]
+        fishes[6] += tmp
+    return sum(fishes)
+                
+if __name__ == "__main__":
+    vals = read_file()
+    print(f"Part 1: {part1(vals)}")
+    print(f"Part 2: {part2(vals)}")
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diff --git a/2021/06/input.txt b/2021/06/input.txt
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+1,1,3,5,3,1,1,4,1,1,5,2,4,3,1,1,3,1,1,5,5,1,3,2,5,4,1,1,5,1,4,2,1,4,2,1,4,4,1,5,1,4,4,1,1,5,1,5,1,5,1,1,1,5,1,2,5,1,1,3,2,2,2,1,4,1,1,2,4,1,3,1,2,1,3,5,2,3,5,1,1,4,3,3,5,1,5,3,1,2,3,4,1,1,5,4,1,3,4,4,1,2,4,4,1,1,3,5,3,1,2,2,5,1,4,1,3,3,3,3,1,1,2,1,5,3,4,5,1,5,2,5,3,2,1,4,2,1,1,1,4,1,2,1,2,2,4,5,5,5,4,1,4,1,4,2,3,2,3,1,1,2,3,1,1,1,5,2,2,5,3,1,4,1,2,1,1,5,3,1,4,5,1,4,2,1,1,5,1,5,4,1,5,5,2,3,1,3,5,1,1,1,1,3,1,1,4,1,5,2,1,1,3,5,1,1,4,2,1,2,5,2,5,1,1,1,2,3,5,5,1,4,3,2,2,3,2,1,1,4,1,3,5,2,3,1,1,5,1,3,5,1,1,5,5,3,1,3,3,1,2,3,1,5,1,3,2,1,3,1,1,2,3,5,3,5,5,4,3,1,5,1,1,2,3,2,2,1,1,2,1,4,1,2,3,3,3,1,3,5
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diff --git a/2021/06/solution.txt b/2021/06/solution.txt
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+++ b/2021/06/solution.txt
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+Part 1: 361169
+Part 2: 1634946868992
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diff --git a/2021/06/test_code.py b/2021/06/test_code.py
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+# SPDX-License-Identifier: MIT
+# Copyright (c) 2021 Akumatic
+
+from code import part1, part2, read_file
+
+def test():
+    vals = read_file("test_input.txt")
+    assert part1(vals, days=18) == 26
+    assert part1(vals) == 5934
+    print("Passed Part 1")
+    assert part2(vals) == 26984457539
+    print("Passed Part 2")
+
+if __name__ == "__main__":
+    test()
diff --git a/2021/06/test_input.txt b/2021/06/test_input.txt
new file mode 100644
index 0000000..a7af2b1
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+++ b/2021/06/test_input.txt
@@ -0,0 +1 @@
+3,4,3,1,2
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diff --git a/2021/README.md b/2021/README.md
index 532a33d..1457d19 100644
--- a/2021/README.md
+++ b/2021/README.md
@@ -20,7 +20,7 @@ Collect stars by solving puzzles. Two puzzles will be made available on each day
 | 03 | :white_check_mark: | :white_check_mark: | [Solution](03/code.py) | [Day 03](https://adventofcode.com/2021/day/3) |
 | 04 | :white_check_mark: | :white_check_mark: | [Solution](04/code.py) | [Day 04](https://adventofcode.com/2021/day/4) |
 | 05 | :white_check_mark: | :white_check_mark: | [Solution](05/code.py) | [Day 05](https://adventofcode.com/2021/day/5) |
-| 06 |  |  |  |  |
+| 06 | :white_check_mark: | :white_check_mark: | [Solution](06/code.py) | [Day 06](https://adventofcode.com/2021/day/6) |
 | 07 |  |  |  |  |
 | 08 |  |  |  |  |
 | 09 |  |  |  |  |