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 A212783 #10 Jul 21 2018 10:06:14 %S A212783 5,27,99,252,546,1034,1803,2925,4517,6670,9528,13204,17869,23655, %T A212783 30763,39344,49626,61782,76067,92673,111885,133914,159072,187592, %U A212783 219813,255987,296483,341572,391650,447010,508075,575157,648709,729062,816696,911964 %N A212783 Half the number of 0..n arrays of length 4 with second differences nonzero. %C A212783 Row 2 of A212782. %H A212783 R. H. Hardin, <a href="/A212783/b212783.txt">Table of n, a(n) for n = 1..210</a> %F A212783 Empirical: a(n) = 2*a(n-1) + a(n-2) - 3*a(n-3) - a(n-4) + a(n-5) + 3*a(n-6) - a(n-7) - 2*a(n-8) + a(n-9). %F A212783 Empirical g.f.: x*(5 + 17*x + 40*x^2 + 42*x^3 + 29*x^4 + 9*x^5 + 2*x^6) / ((1 - x)^5*(1 + x)^2*(1 + x + x^2)). - _Colin Barker_, Jul 21 2018 %e A212783 Some solutions for n=5: %e A212783 ..5....4....2....3....5....4....0....4....2....4....2....1....5....1....4....4 %e A212783 ..4....5....2....4....1....2....1....0....3....1....2....4....0....0....4....5 %e A212783 ..1....0....1....0....3....5....1....2....1....4....5....2....2....1....0....5 %e A212783 ..0....4....4....3....4....2....3....0....0....3....3....1....2....3....0....3 %Y A212783 Cf. A212782. %K A212783 nonn %O A212783 1,1 %A A212783 _R. H. Hardin_, May 27 2012