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 A212776 #9 Jul 22 2025 22:57:08 %S A212776 11,27,66,162,397,973,2385,5846,14329,35122,86088,211011,517211, %T A212776 1267741,3107372,7616509,18668898,45759514,112161581,274920321, %U A212776 673859821,1651704234,4048508001,9923336574,24323184920,59618790539,146132186103 %N A212776 Half the number of 0..2 arrays of length n+2 with second differences nonzero. %C A212776 Column 2 of A212782 %H A212776 R. H. Hardin, <a href="/A212776/b212776.txt">Table of n, a(n) for n = 1..210</a> %F A212776 Empirical: a(n) = a(n-1) +2*a(n-2) +3*a(n-3) +2*a(n-4). %F A212776 Empirical: G.f. -x*(11+16*x+17*x^2+9*x^3) / ( -1+x+2*x^2+3*x^3+2*x^4 ). - _R. J. Mathar_, Jul 01 2013 %e A212776 Some solutions for n=5 %e A212776 ..2....0....1....1....1....2....0....1....0....0....1....2....0....0....1....2 %e A212776 ..0....2....1....2....1....2....1....2....2....2....2....1....2....0....0....0 %e A212776 ..0....1....0....0....0....1....0....1....0....1....1....1....0....2....2....0 %e A212776 ..1....2....0....1....1....1....2....2....0....2....2....2....2....1....0....2 %e A212776 ..1....0....2....1....0....0....1....0....1....0....0....0....0....1....1....0 %e A212776 ..2....1....1....0....2....0....2....1....0....2....2....1....2....0....0....1 %e A212776 ..0....1....2....0....1....1....1....0....0....2....1....0....1....2....1....1 %K A212776 nonn %O A212776 1,1 %A A212776 _R. H. Hardin_ May 27 2012