Find the program that prints this integer sequence (Cops' thread) This is the cops' thread. The robbers' thread goes here.
The last cops-and-robbers thread was already 4 months ago.
The cop's task

The cop's task is to write a program/function that takes a positive (or non-negative) integer and outputs/returns another integer.
The cop must state it if the program is intolerant towards zero.
The cop will provide at least 2 sample inputs/outputs.
For example, if I have decided to write the Fibonacci sequence, I would write this in my answer:


a(0) returns 0
a(3) returns 2


The number of examples is up to the cop's discretion.
However, the sequence must actually exist in the On-Line Encyclopedia of Integer Sequences®, so no pseudo-random number generator for you. :(
The cop can hide as many characters as is so wished.
For example, if my program is:


function a(n)
    if n&gt;2 then
        return n
    else
        return a(n-1) + a(n-2)
    end
end



Then I would hide these characters as I want:


function a(n)
    if ### then
        ########
    else
        ######################
    end
end


The robber's task

is obviously to find the original source code.
However, any proposed source code that produces the same set of output also counts as valid, as long as it is also found in OEIS.


Tips for the cops

The search function in the OEIS only works for consecutive terms, so if you want to hide your sequence, then just leave a hole anywhere.
Apparently there is no way to hide the sequence. Put this in mind when you choose the sequence.


Your score is the number of bytes in your code.
The winner will be the submission with the lowest score that hasn't been cracked in 7 days.
Only submissions that are posted in 2016 April are eligible for the win. Submissions that are posted later than this are welcome, but cannot win.
In order to claim the win you need to reveal the full code and the OEIS sequence (after 7 days).
Your post should be formatted like this (NN is the number of characters):

Lua, 98 bytes
Output:
a(0) returns 0
a(3) returns 2

Code (# marks unrevealed characters):
function a(n)
    if ### then
        ########
    else
        ######################
    end
end


If the code is cracked, insert [Cracked](link to cracker) in the header.
If the submission is safe, insert &quot;Safe&quot; in the header and reveal the full code in your answer. Only answers that have revealed the full code will be eligible for the win.
Vim, 36 keystrokes -- Safe!

i****&lt;esc&gt;:let @q="^*i****$**@***"&lt;cr&gt;&lt;n&gt;@qbD


(Note: &lt;n&gt; is where you type your input)

Here is the code unrelated to number generation:

          :let @q="              "&lt;cr&gt;&lt;n&gt;@qbD


Meaning I am revealing 5 out of 19 characters.

&lt;n&gt; is the input. Here are some sample outputs:

1@q:    1
2@q:    3
6@q:    18


Answer

This code prints The Lucas Numbers (A000032), which are just like The Fibonnaci Sequence, except that it starts on 2, 1 instead of 1, 1. Here are the first 15 numbers:

2, 1, 3, 4, 7, 11, 18, 29, 47, 76, 123, 199, 322, 521, 843


Here's the revealed code:

i2 1 &lt;esc&gt;:let @q="^diwwyw$pb@-&lt;c-v&gt;&lt;c-a&gt;"&lt;cr&gt;&lt;n&gt;@qbD


Explanation:

i2 1 &lt;esc&gt;                          "Insert the starting numbers
          :let @q="....."&lt;cr&gt;       "Define the macro 'Q'


Explanation of the macro:

^                      "Move to the first non-whitespace character on the line.
 diw                   "(d)elete (i)nner (w)ord. This is different then 'dw' because it doesn't grab the space. 
                      "It also throws people off since 'i' is usually used for inserting text.
    wyw$               "Move to the next number, yank it then move to the end of the line 
        pb             "(p)aste the yanked text and move (b)ack
          @-     &lt;c-a&gt; "@- is the register holding the word we deleted. Increment the current number that many times.
            &lt;c-v&gt;      "Since we're adding &lt;c-a&gt; this from the command line, we need to type it as a literal.


Now, we just need to remove the second number, since the first number is the lucas number we want. So we do

b   "move (b)ack
 D  "(D)elete to the end of the line.


Also, if I'm not mistaken, this is the first safe submission! That's kinda cool.