Change the Code, Change the Sequence: Cops This is a cops-and-robbers challenge. For the robbers thread, go here.

This challenge involves two OEIS sequences chosen by the cops -- S1, S2 -- and how well those sequences can be golfed and obfuscated.

The Cops' Challenge

Your challenge as a cop is to pick a freely available language, and two OEIS sequences. Then, write code A in that language that takes input n and produces S1(n). When that code is modified by a Levenshtein distance of X characters (with X no more than 0.5 * (length A)), and turned into code B in the same language, it must then produce S2(n). You must actually write this code B, but don't reveal it until your challenge is safe (see below).

The cops' submissions must include the language name, the full code A, the byte-count of A, the X value of how many changes to get to their secret B code, and the chosen S1 and S2 sequence numbers. You can choose whether each sequence is 0-indexed or 1-indexed, but please specify that in your submission.

To crack a particular submission, robbers must come up with a program C in the same language (and version) that produces S2(n) and is Y character changes away from A (with Y &lt;= X). Robbers do not necessarily need to find the exact same B code that the cop (secretly) produced.

Winning and Scoring

If your cop answer has not been cracked within 7 days (168 hours), you may reveal your own B solution, at which point your answer is considered safe. As long as you don't reveal your solution, it may still be cracked by robbers, even if the 7 days have already passed. If your answer does get cracked, please indicate this in the header of your answer, along with a link to the corresponding robber's answer.

Cops win by having the uncracked submission with the shortest A. If tied, then the smallest X will be used as tie-breaker. If still tied, the earlier submission will win.

Further Rules


You must not use any built-ins for hashing, encryption, or random number generation (even if you seed the random number generator to a fixed value).
Either programs or functions are allowed, but the code must not be a snippet and you must not assume a REPL environment.
You may take input and give output in any convenient format. The input/output methods must be the same for both sequences.
The definitive calculator for the Levenshtein distance for this challenge is this one on Planet Calc.
In addition to being a CnR challenge, this is code-golf so all usual golfing rules apply.
Brain-Flak, 28 bytes, Distance of 4, A002817, A090809 Cracked
This answer uses 1-indexing
(({({}[()])}{}){({}[()])}{})

Try it online
For anyone interested there are 27475 valid Brain-Flak programs with Levenshtein distance 4 from this program and 27707 with distance 4 or less.  So a brute force solution would be feasible on a consumer grade computer.