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 A131246 #13 Aug 26 2015 00:45:53
%S A131246 1,3,6,13,27,57,119,250,523,1097,2297,4815,10086,21137,44283,92793,
%T A131246 194419,407378,853559,1788481,3747361,7851867,16451910,34471669,
%U A131246 72228171,151339401,317100335,664418698,1392152131
%N A131246 Row sums of triangle A131245.
%C A131246 A131244 is a companion sequence.
%H A131246 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (1,3,-1,-1)
%F A131246 G.f. -(1+x)*(x^2-x-1)/ ( 1-x-3*x^2+x^3+x^4 ). - _R. J. Mathar_, Jan 29 2011
%F A131246 a(0)=1, a(1)=3, a(2)=6, a(3)=13, a(n)=a(n-1)+3*a(n-2)-a(n-3)-a(n-4). - _Harvey P. Dale_, Sep 07 2013
%e A131246 a(3) = 13 = sum of row 3 terms of triangle A131245: (5 + 5 + 2 + 1)
%p A131246 A046854 := proc(n,k) binomial(floor((n+k)/2),k) ; end proc:
%p A131246 A131245 := proc(n,k) local a,j ; a := 0 ; for j from k to n do a := a+ A046854(n,j)*A046854(j,k) ; end do: a ; end proc:
%p A131246 A131246 := proc(n) add(A131245(n,k),k=0..n) ; end proc:
%p A131246 seq(A131246(n),n=0..50) ; # _R. J. Mathar_, Jan 29 2011
%t A131246 CoefficientList[Series[-(1+x)(x^2-x-1)/(1-x-3x^2+x^3+x^4),{x,0,30}],x] (* or *) LinearRecurrence[{1,3,-1,-1},{1,3,6,13},30] (* _Harvey P. Dale_, Sep 07 2013 *)
%Y A131246 Cf. A131243, A131244, A131245, A065941, A046854.
%K A131246 nonn
%O A131246 0,2
%A A131246 _Gary W. Adamson_, Jun 22 2007