><>, 276 bytes (Cracked)
1$1-:?!v$: 1[0$ >:?!va2[$:{:@%:{$-{,]v
>$n; v < ^ >~{]02.1+1+ffr+1r<
:}[r]{ [01>:{*@@+$a*l2=?!^~]+ff+9+1g"3"=?v"3"ff+9+1pf0.
:}[l01-$> $:0(?v$@$:@@:@)?v@@1-$}v >"2"ff+9+1p00.
>. ^-1l v!?} < .4a}$@@$< .4a<
^26{]r0[}:{]~{<
Try it online! Call this one with -v n
to get the n-th element (1-indexed)
1$1-:?!;$::n84*o1[0$ >:?!va2[$:{:@%:{$-{,]v
v < ^ >~{]02.1+1+ffr+1r<
:}[r]{ [01>:{*@@+$a*l2=?!^~]+ff+9+1g"3"=?v"3"ff+9+1pf0.
:}[l01-$> $:0(?v$@$:@@:@)?v@@1-$}v >"2"ff+9+1p00.
>. ^-1l v!?} < .4a}$@@$< .4a<
^26{]r0[}:{]~{<
Try it online! Call with -v n
to get a list of n-1 elements starting at 1
A long and complex one, this is OEIS A004000.
Let a(n) = k, form m by Reversing the digits of k, Add m to k Then Sort the digits of the sum into increasing order to get a(n+1).
Example: 668 -> 668 + 866 = 1534 -> 1345.
Because the code in ><> is quite long, the challenge is to crack it for \$n = 34\$.
These 34 elements make a total of 290 bytes, just a bit too much to hardcode the result ;)
Here are the 34 first elements 1-indexed
1 2 4 8 16 77 145 668 1345 6677 13444 55778 133345 666677 1333444 5567777 12333445 66666677 133333444 556667777 1233334444 5566667777 12333334444 55666667777 123333334444 556666667777 1233333334444 5566666667777 12333333334444 55666666667777 123333333334444 556666666667777 1233333333334444 5566666666667777