Golfing Chain (Cops' Thread)

Question

This is a Cops and Robbers challenge. For the Robbers' thread, go here.

The Cops have three tasks.
1) Pick a sequence from the OEIS.

2) Pick a language (this is suggested to be a golflang, but doesn't have to be) that, when given input n, outputs A(n) (where A(n) is the sequence chosen) using all usual code-golf rules.
Call this language L_A and code C_A.
For example, Jelly and Jelly_code.

3) Then, pick a different language (this is suggested to be a non-golflang, but doesn't have to be) and write code that takes no input and outputs code C_A, again following all usual code-golf rules. (Note: this can be obfuscated code and doesn't necessarily need to be golfed, but the longer this code is the easier it will be for the robbers to crack your submission.)
Call this language L_B and code C_B.
For example, Python and Python_code.

The Cop's submission to this challenge is the sequence (specified whether 0- or 1-indexed), the name of the two languages L_A and L_B (and which one solves which part), and the byte-count of C_B only. Keep the actual code of both parts, and the length of C_A, secret.

For the Cop, links to documentation for L_A and L_B, or an interpreter (or a TIO link, since that includes both), are appreciated but not required.

The Robber's challenge is to select a Cops' entry and write code C_C in the same L_B language that outputs some code in the same L_A language that solves the original OEIS task. The length of C_C can be no longer than the length of C_B as revealed by the cop (though may be shorter). Note: The code produced by C_C does not have to match C_A.

For our example, this means that the Robber has to write Python code that outputs Jelly code that solves the original OEIS sequence, and that Python code has to be no longer than the length revealed by the Cop.

Winning conditions

Answers that have not been cracked in a week can have their solutions revealed, at which point they are considered Safe. Note that if you don't reveal your solution after a week, it can still be cracked. The Cop with the shortest Safe answer wins.

Answer 1

OEIS A000041, cracked by ETHproductions

Let's try it the other way around: golflang generates non-golflang.

a(n) = number of partitions of n (the partition numbers).

• a(n) (0-indexed) is returned by a JavaScript function (ES6)
• The program that outputs the JS function is written in Jelly
• The length of the Jelly program is 35 bytes

Intended solution

Jelly: “¦ṚoIwƭ- ḊFæSḂ¥¶Ẉ|ḊJƓƝʋnrB⁾’b28+40Ọ

which outputs

JS: C=(A,B=A)=>A<0?0:A?B?C(A,B-1)+C(A-B,B):0:1

Answer 2

OEIS 000035, cracked by betseg

The problem is solved in Proton.
The Proton code is output by Python.
The length of the Python program is 13 bytes.

Really easy one for starters (if you know Proton :D). Zero-indexed.

Intended Solution

Python: print("(2%)")
Proton: (2%)
Though I decided to let n=>n%2 be short enough because dyadic/monadic function shortcuts are not documented.

Answer 3

OEIS A048272, cracked by DJMcMayhem

Number of odd divisors of n minus number of even divisors of n (1-indexed).

• The program that outputs a(n) is written in 05AB1E.
• The program that outputs the 05AB1E program is written in Brain-Flak + the -A flag.
• The length of the Brain-Flak program is 198 bytes (the byte count does not include the flag).

Note that I could probably easily golf the Brain-Flak program by using stack-manipluation tricks and other kolmogorov-complexity tricks I am aware of, but I wanted to keep this simple as my first submission. Good luck, robbers!

What I had in mind

05AB1E: ÑÈD<)O(O

Brain-Flak: (((((((((((()()()){}){}){({}[()])}{}())[((((()()()){}){}())){}{}])((((()()()){}){}())){}{})[((((()()()){}){})()){}{}])(((()()()){})){}{}())(()()()()){})(((((()()()()){}){}){}()){}){})((()()())){}{})

Answer 4

OEIS A000034 (cracked by H.PWiz)

1, 2, 1, 2, 1, 2, 1, 2, …

Period 2: repeat [1, 2]; a(n) = 1 + (n mod 2).

a(n) is the output of a Haskell answer, which is the output of a 32-byte Malbolge answer.

Answer 5

OEIS A000668, cracked by Lynn

Mersenne primes (of form 2^p-1 where p is a prime)

• a(n) is outputted by a Jelly full program.
• n is 1-indexed.
• The Jelly program is printed by a Triangularity program, whose length is 38 bytes.

Different strategy: solve the sequence in a golflang and output the program in an esolang.

Intended solution

• Jelly code
• Triangularity code

Answer 6

OEIS A055642, cracked by Lynn

Number of digits in decimal expansion of n

This is probably too easy, but it took me a while so I hope someone out there will be just as disappointed as I was when I finally figured it out :D

• The program that writes out a(n) is written in 05AB1E
• The program that prints the 05AB1E program is written in TeX
• The TeX program is 6 bytes long

What I had in mind:

Sg as 05AB1E code
Sg\bye as TeX code