Chip, 67 bytes, cracked by Yimin Rong
2D5B#{*Cm49!}E-7 (A000012d#,zkmsh b-\6/e2)[1Zv^~^S 33a#kcf3g88taz1@ A000012. A bit cheeky, yes.
Uses bytes for i/o, so I was nice and built a bashy/pythony wrapper.
Alternate sequence is A060843. Try it online for inputs
1..4.
Yimin Rong hunched right, such a short Chip program can only calculate very simple things. The original sequence is all one's, and the alternate sequence is the busy beaver numbers, of which only 4 are known.
These numbers,1, 6, 21, 107, are simply hard-coded for the inputs1..4.
One interesting thing about using Chip for this challenge is that the digits0-9are not numbers, but logical elements. Specifically,0-7are the eight bits addressing the head of the stack, and8and9are the read and write toggles. That made this a bit more interesting and much more obfuscated.
A potential giveaway is that onlyA-Dappear, meaning that we only have 4 bits for indexing the sequence. This meant that there could be at most 16 different values. In fact, onlyA-Care actually used for the alternate sequence, giving at most 8 different values.
For any who might be interested, here is the same code, stripped of the no-ops and unused elements:
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B *C 49! A000012d ,z s b-\6/e 1Zv-~^S `3a`-cf3g`8taz1