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 A141499 #12 Jun 13 2015 00:52:39
%S A141499 0,1,10,45,190,780,3160,12720,51040,204480,818560,3275520,13104640,
%T A141499 52423680,209704960,838840320,3355402240,13421690880,53686927360,
%U A141499 214748037120,858992803840,3435972526080,13743892725760,54975576145920,219902315069440,879609281249280
%N A141499 a(0)=0; a(1)=1; a(n) = triangular number at index 5*2^(n-2)-1.
%C A141499 The sequence a(n)=b(n)*(b(n)-1)/2 gives an SO(2),SO(5),SO(10),SO(20), ...
%H A141499 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (6,-8).
%F A141499 a(0)=0. a(n)=A000217(A052549(n-1)), n>0. - _R. J. Mathar_, Oct 29 2008
%F A141499 a(n)=5*2^(-5+n)*(-4+5*2^n) for n>1. a(n)=6*a(n-1)-8*a(n-2) for n>3. G.f.: x*(1+4*x-7*x^2)/((1-2*x)*(1-4*x)). [_Colin Barker_, Aug 16 2012]
%t A141499 Clear[a] a[0] = 1; a[1] = 2; a[2] = 5; a[n_] := a[n] = a[1]*a[n - 1]; Table[a[n]*(a[n] - 1)/2, {n, 0, 20}]
%t A141499 Join[{0,1},LinearRecurrence[{6,-8},{10,45},30]] (* _Harvey P. Dale_, May 23 2013 *)
%Y A141499 Cf. A084215.
%K A141499 nonn,easy
%O A141499 0,3
%A A141499 _Roger L. Bagula_, Aug 10 2008
%E A141499 Edited by _N. J. A. Sloane_, Aug 16 2008
%E A141499 Corrected the definition, which was describing an auxiliary sequence. - _R. J. Mathar_, Oct 29 2008
%E A141499 More terms from _Harvey P. Dale_, May 23 2013