This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A358258 #21 Nov 07 2022 02:10:12
%S A358258 0,2,6,9,17,42,92,131,307,650,1024,2238,4164,8226,17384,33197,67167,
%T A358258 133549,269119,525974,1055175,2111641,4213053,8444257,16783217,
%U A358258 33601813,67405064,134239260,268711604,538400994,1076155844,2152693259,4299075300,8594396933,17203509931
%N A358258 First n-bit number to appear in Van Eck's sequence (A181391).
%C A358258 Binary version of A358168.
%e A358258 First terms written in binary, substituting "." for 0 to enhance the pattern of 1's.
%e A358258 n a(n) a(n)_2
%e A358258 -------------------------------------
%e A358258 1 0 .
%e A358258 2 2 1.
%e A358258 3 6 11.
%e A358258 4 9 1..1
%e A358258 5 17 1...1
%e A358258 6 42 1.1.1.
%e A358258 7 92 1.111..
%e A358258 8 131 1.....11
%e A358258 9 307 1..11..11
%e A358258 10 650 1.1...1.1.
%e A358258 11 1024 1..........
%e A358258 12 2238 1...1.11111.
%e A358258 13 4164 1.....1...1..
%e A358258 14 8226 1.......1...1.
%e A358258 15 17384 1....11111.1...
%e A358258 16 33197 1......11.1.11.1
%e A358258 17 67167 1.....11..1.11111
%e A358258 18 133549 1.....1..11.1.11.1
%e A358258 19 269119 1.....11.11..111111
%e A358258 20 525974 1........11.1..1.11.
%e A358258 21 1055175 1.......11..111...111
%e A358258 22 2111641 1.......111...1..11..1
%e A358258 23 4213053 1.......1..1..1..1111.1
%e A358258 24 8444257 1.......11.11..1.11....1
%t A358258 nn = 2^20; q[_] = False; q[0] = True; a[_] = 0; c[_] = -1; c[0] = 2; m = 1; {0}~Join~Rest@ Reap[Do[j = c[m]; k = m; c[m] = n; m = 0; If[j > 0, m = n - j]; If[! q[#], Sow[k]; q[#] = True] & @ IntegerLength[k, 2], {n, 3, nn}] ][[-1, -1]]
%o A358258 (Python)
%o A358258 from itertools import count
%o A358258 def A358258(n):
%o A358258 b, bdict, k = 0, {0:(1,)},1<<n-1 if n > 1 else 0
%o A358258 for m in count(2):
%o A358258 if b >= k:
%o A358258 return b
%o A358258 if len(l := bdict[b]) > 1:
%o A358258 b = m-1-l[-2]
%o A358258 if b in bdict:
%o A358258 bdict[b] = (bdict[b][-1],m)
%o A358258 else:
%o A358258 bdict[b] = (m,)
%o A358258 else:
%o A358258 b = 0
%o A358258 bdict[0] = (bdict[0][-1],m) # _Chai Wah Wu_, Nov 06 2022
%Y A358258 Cf. A181391, A358168, A358180, A358259.
%K A358258 nonn,base
%O A358258 1,2
%A A358258 _Michael De Vlieger_, Nov 05 2022
%E A358258 a(30)-a(34) from _Chai Wah Wu_, Nov 06 2022
%E A358258 a(35) from _Martin Ehrenstein_, Nov 07 2022