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 A336861 #28 Sep 08 2022 08:46:25
%S A336861 0,0,0,1,1,2,2,2,3,3,4,4,5,5,5,6,6,7,7,8,8,9,9,9,10,10,11,11,12,12,13,
%T A336861 13,14,14,14,15,15,16,16,17,17,18,18,19,19,20,20,20,21,21,22,22,23,23,
%U A336861 24,24,25,25,26,26,27,27,27,28,28,29,29,30,30,31,31,32
%N A336861 a(n) = ceiling((n-1-sqrt(n+1))/2).
%C A336861 a(n) is a lower bound for the number of items outside the instance of n-1 at one end of a Colombian variant Langford pairing (A336747). For example, one of the most lop-sided pairings for n=7 is 4 1 6 1 7 4 3 5 2 6 3 2 7 5, and there are a(n)=2 items to the left of the first '6'. This bound is tight until at least n=184.
%H A336861 Edward Moody, <a href="https://github.com/EdwardMGraphite/colombian-langford">Java program for enumerating Colombian Langford pairings</a>
%t A336861 Table[Ceiling[(n - 1 - Sqrt[n + 1])/2], {n, 1, 100}] (* _Amiram Eldar_, Aug 21 2020 *)
%o A336861 (Magma) [Ceiling((n-1-Sqrt(n+1))/2) : n in [1..100]]; // _Wesley Ivan Hurt_, Aug 21 2020
%o A336861 (PARI) a(n) = ceil((n-1-sqrt(n+1))/2); \\ _Michel Marcus_, Aug 19 2020
%Y A336861 Cf. A336747.
%K A336861 nonn,easy
%O A336861 1,6
%A A336861 _Edward Moody_, Aug 16 2020