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 A385683 #13 Aug 06 2025 12:03:49 %S A385683 1,3,4,5,7,8,9,11,12,13,14,15,17,18,19,20,21,22,23,25,26,27,28,29,30, %T A385683 31,33,34,35,36,37,38,39,40,41,43,44,45,46,47,48,49,50,51,52,53,55,56, %U A385683 57,58,59,60,61,62,63,64,65,67,68,69,70,71,72,73,74,75,76 %N A385683 Complement of A030511. %C A385683 Positive numbers not of the form floor(2*k^2/3). %F A385683 a(n) = n+m if n+m>floor(2*(m+1)^2/3) and a(n) = n+m-1 otherwise where m = floor(sqrt(3*(n-1)/2)). %t A385683 m[n_]:=Floor[Sqrt[3(n-1)/2]];a[n_]:=If[n+m[n]>Floor[2(m[n]+1)^2/3],n+m[n],n+m[n]-1];Array[a,67] (* _James C. McMahon_, Aug 06 2025 *) %o A385683 (Python) %o A385683 from math import isqrt %o A385683 def A385683(n): return n+(m:=isqrt(3*(n-1)>>1))-(n+m<=((m+1)**2<<1)//3) %Y A385683 Cf. A030511. %K A385683 nonn,easy %O A385683 1,2 %A A385683 _Chai Wah Wu_, Aug 04 2025