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 A255667 #6 Jul 23 2025 15:09:44 %S A255667 65536,262144,1020000,3083292,7323894,15269184,29577432,53275408, %T A255667 90990131,149141772,236469626,364664160,549120490,809830656, %U A255667 1172434356,1669450392,2341713998,3240048488,4427203308,5980094628,7992389097 %N A255667 Number of length n+7 0..3 arrays with at most two downsteps in every n consecutive neighbor pairs. %C A255667 Row 7 of A255660 %H A255667 R. H. Hardin, <a href="/A255667/b255667.txt">Table of n, a(n) for n = 1..210</a> %F A255667 Empirical: a(n) = (1/39916800)*n^11 + (13/3628800)*n^10 + (1/4320)*n^9 + (211/24192)*n^8 + (1428221/1209600)*n^7 + (5660089/172800)*n^6 + (145503607/362880)*n^5 + (63892553/36288)*n^4 + (439312849/7200)*n^3 - (2124832139/12600)*n^2 + (67026258/385)*n - 159592 for n>5 %e A255667 Some solutions for n=1 %e A255667 ..2....1....1....1....0....3....0....3....0....2....3....0....2....3....2....2 %e A255667 ..0....3....2....1....2....0....1....3....1....1....3....2....3....2....3....0 %e A255667 ..1....0....0....0....0....2....2....3....3....2....1....1....1....0....0....1 %e A255667 ..1....2....0....3....2....1....3....1....2....2....2....1....1....2....1....3 %e A255667 ..1....1....1....0....1....1....1....3....3....3....3....0....3....0....2....0 %e A255667 ..1....3....2....1....3....3....0....2....3....0....1....3....0....1....3....1 %e A255667 ..2....0....0....0....3....2....0....2....1....2....2....0....2....3....3....2 %e A255667 ..1....3....0....0....3....1....0....0....1....0....0....1....1....0....0....1 %Y A255667 Cf. A255660 %K A255667 nonn %O A255667 1,1 %A A255667 _R. H. Hardin_, Mar 01 2015