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 A050135 #14 Oct 15 2019 11:51:51 %S A050135 1,8,4,2,20,10,5,32,16,40,44,22,11,56,28,14,7,3,76,38,19,9,92,46,23, %T A050135 104,52,26,13,6,124,62,31,15,140,70,35,17,156,78,39,168,84,42,21,184, %U A050135 188,94,47,200,100,50,25,12,220,110,55,27,236 %N A050135 a(1) = 1, a(n) = floor(a(n-1)/2) if this is not among 0,a(1),...,a(n-1); otherwise a(n) = 4*n. %C A050135 Does this sequence contain every positive integer exactly once? %Y A050135 Cf. A050000. %K A050135 nonn %O A050135 1,2 %A A050135 _Clark Kimberling_