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 A047839 #17 Sep 08 2022 08:44:57
%S A047839 2,4,5,6,8,9,10,12,13,14,15,16,18,19,20,21,22,24,25,26,27,28,29,30,32,
%T A047839 33,34,35,36,37,38,40,41,42,43,44,45,46,47,48,50,51,52,53,54,55,56,57,
%U A047839 58,60,61,62,63,64,65,66,67,68,69,70,72,73,74,75,76,77,78,79
%N A047839 a(n) = n + floor( sqrt(2*n) ).
%C A047839 Complement of A047838.
%H A047839 G. C. Greubel, <a href="/A047839/b047839.txt">Table of n, a(n) for n = 1..10000</a>
%t A047839 Table[n +Floor[Sqrt[2*n]], {n,1,100}] (* _G. C. Greubel_, Sep 08 2018 *)
%o A047839 (PARI) {a(n) = if( n<0, 0, n + sqrtint(2*n))}
%o A047839 (Magma) [n +Floor(Sqrt(2*n)): n in [1..100]]; // _G. C. Greubel_, Sep 08 2018
%Y A047839 Cf. A047838.
%K A047839 nonn,easy
%O A047839 1,1
%A A047839 _Michael Somos_, May 07 1999