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 A212778 #8 Jul 21 2018 10:06:07 %S A212778 56,252,1134,5104,22972,103391,465336,2094360,9426184,42424863, %T A212778 190943548,859388488,3867889651,17408390437,78350750657,352636859298, %U A212778 1587129076523,7143265484325,32150026443551,144699115914141,651254025656788 %N A212778 Half the number of 0..4 arrays of length n+2 with second differences nonzero. %C A212778 Column 4 of A212782. %H A212778 R. H. Hardin, <a href="/A212778/b212778.txt">Table of n, a(n) for n = 1..210</a> %F A212778 Empirical: a(n) = 2*a(n-1) + 7*a(n-2) + 14*a(n-3) + 19*a(n-4) + 18*a(n-5) + 5*a(n-6) - 5*a(n-7) - 2*a(n-8). %F A212778 Empirical g.f.: x*(56 + 140*x + 238*x^2 + 288*x^3 + 234*x^4 + 47*x^5 - 68*x^6 - 25*x^7) / (1 - 2*x - 7*x^2 - 14*x^3 - 19*x^4 - 18*x^5 - 5*x^6 + 5*x^7 + 2*x^8). - _Colin Barker_, Jul 21 2018 %e A212778 Some solutions for n=5: %e A212778 ..3....3....3....0....3....3....0....4....0....3....2....2....1....0....1....4 %e A212778 ..3....3....0....4....4....0....4....0....1....2....0....2....3....0....0....3 %e A212778 ..2....0....3....0....4....1....3....3....1....2....3....4....2....4....1....1 %e A212778 ..2....4....1....0....2....0....1....0....2....4....4....2....2....3....3....0 %e A212778 ..3....3....3....1....4....4....2....3....4....2....1....1....0....0....3....2 %e A212778 ..2....4....2....3....4....4....2....3....2....4....4....1....4....0....4....3 %e A212778 ..4....1....2....0....0....2....0....0....2....0....4....4....3....3....0....1 %Y A212778 Cf. A212782. %K A212778 nonn %O A212778 1,1 %A A212778 _R. H. Hardin_, May 27 2012