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 A049858 #22 Feb 04 2025 18:33:30
%S A049858 0,1,2,3,5,9,17,32,60,112,209,390,728,1359,2537,4736,8841,16504,30809,
%T A049858 57513,107363,200421,374138,698426,1303794,2433871,4543454,8481540,
%U A049858 15833003,29556423,55174760,102998057,192272694,358927051,670030805,1250786973,2334919589
%N A049858 a(n) = Sum{a(k): k=0,1,2,...,n-4,n-2,n-1}; a(n-3) is not a summand; initial terms are 0,1,2.
%H A049858 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-1,1).
%F A049858 a(n) = 2*a(n-1) -a(n-3) +a(n-4).
%F A049858 G.f. x*(x-1)*(1+x) / ( -1+2*x-x^3+x^4 ). - _R. J. Mathar_, Nov 12 2012
%F A049858 a(n) = A059633(n+2)-A059633(n). - _R. J. Mathar_, Aug 16 2017
%o A049858 (PARI) a(n)=([0,1,0,0; 0,0,1,0; 0,0,0,1; 1,-1,0,2]^n*[0;1;2;3])[1,1] \\ _Charles R Greathouse IV_, Aug 16 2017
%Y A049858 Pairwise sums of A049856. Partial sums of A049864.
%K A049858 nonn,easy
%O A049858 0,3
%A A049858 _Clark Kimberling_