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 A018930 #29 Oct 11 2013 20:31:53
%S A018930 3,4,12,84,132,12324,1836,105552,255084,197580,10358340,13775220,
%T A018930 1936434780,51299286012,123205977516,862441842612,1310543298204,
%U A018930 667510076211780,207181940072172,110912831751840,1698410314006284
%N A018930 a(1)=3; for n>1, a(n) is smallest positive integer such that a(1)^2+...+a(n)^2 = m^2 for some m.
%H A018930 Vincenzo Librandi, <a href="/A018930/b018930.txt">Table of n, a(n) for n = 1..100</a>
%t A018930 f[n_]:=Module[{a={3}}, Do[AppendTo[a,First[y/. {ToRules[Reduce[{y^2+a.a == x^2,x>0,y>0}, {y,x},Integers]]}]], {n-1}]; a]; f[21]//Timing (* _Jean-François Alcover_, Jan 26 2007 *)
%o A018930 (PARI) print1("3, "); s=9; for(n=1,30, d=divisors(s); t=d[#d\2]; q=(s\t-t)/2; print1(q,", "); s+=q^2); \\ _Max Alekseyev_, Nov 23 2012
%Y A018930 Cf. A018928, A018929, A127689.
%K A018930 nonn
%O A018930 1,1
%A A018930 Charles Reed (charles.reed(AT)bbs.ewgateway.org)
%E A018930 More terms from _David W. Wilson_.