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 A076816 #5 Mar 02 2015 16:08:49
%S A076816 0,0,1,3,1,4,0,4,9,3,9,1,8,16,6,15,3,13,24,10,22,6,19,1,15,30,10,26,4,
%T A076816 21,39,15,34,8,28,0,21,43,13,36,4,28,53,19,45,9,36,64,26,55,15,45,3,
%U A076816 34,66,22,55,9,43,78,30,66,16,53,1,39,78,24,64,8,49,91,33,76,16,60,105,43
%N A076816 Squares modulo triangular numbers: n^2 minus the greatest triangular number smaller than or equal to n^2.
%H A076816 Harvey P. Dale, <a href="/A076816/b076816.txt">Table of n, a(n) for n = 0..1000</a>
%F A076816 a(n)=n^2-floor(sqrt(2*n^2+1/4)-1/2)*floor(sqrt(2*n^2+1/4)+1/2)/2
%p A076816 seq(n^2-floor(sqrt(2*n^2+1/4)-1/2)*floor(sqrt(2*n^2+1/4)+1/2)/2,n=0..100);
%t A076816 smt[n_]:=Module[{x=Floor[(Sqrt[1+8n]-1)/2]},n-(x(x+1))/2]; smt/@(Range[ 0,80]^2) (* _Harvey P. Dale_, May 12 2014 *)
%Y A076816 Cf. A064784.
%K A076816 nonn,easy
%O A076816 0,4
%A A076816 _Floor van Lamoen_, Oct 17 2002