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 A024220 #15 Jun 25 2019 22:21:39
%S A024220 2,19,71,188,410,784,1367,2226,3435,5078,7249,10049,13589,17990,23380,
%T A024220 29897,37689,46911,57728,70315,84854,101537,120566,142150,166508,
%U A024220 193869,224469,258554,296380,338210,384317,434984,490501,551168,617295,689199
%N A024220 a(n) = [ (3rd elementary symmetric function of S(n))/(first elementary symmetric function of S(n)) ], where S(n) = {first n+2 positive integers congruent to 1 mod 3}.
%F A024220 Conjecture: a(n) = 4*a(n-1) - 6*a(n-2) + 5*a(n-3) - 5*a(n-4) + 6*a(n-5) - 4*a(n-6) + a(n-7). G.f.: x*(-2-11*x-7*x^2-8*x^3+x^4) / ( (1+x+x^2)*(x-1)^5 ). - _R. J. Mathar_, Oct 08 2011
%F A024220 a(n) = floor(A024213(n) / A000326(n+2)). - _Sean A. Irvine_, Jun 25 2019
%K A024220 nonn
%O A024220 1,1
%A A024220 _Clark Kimberling_