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 A223956 #6 Jul 23 2025 04:41:15 %S A223956 20,295,3471,41006,485714,5777663,68892600,822141033,9813968785, %T A223956 117159879996,1398692077165,16698106010927,199348287106117, %U A223956 2379894628461976,28412070357384947,339193873130519142 %N A223956 Number of nX3 0..3 arrays with antidiagonals unimodal and rows and diagonals nondecreasing. %C A223956 Column 3 of A223961 %H A223956 R. H. Hardin, <a href="/A223956/b223956.txt">Table of n, a(n) for n = 1..210</a> %F A223956 Empirical: a(n) = 20*a(n-1) -105*a(n-2) +51*a(n-3) +589*a(n-4) +1340*a(n-5) -8833*a(n-6) -2855*a(n-7) +30423*a(n-8) +57774*a(n-9) -140760*a(n-10) -176184*a(n-11) +106272*a(n-12) +544320*a(n-13) %e A223956 Some solutions for n=3 %e A223956 ..1..3..3....0..1..1....0..1..3....2..2..3....1..1..1....0..3..3....0..0..0 %e A223956 ..0..2..3....1..1..2....0..2..2....1..3..3....1..2..2....1..3..3....0..0..0 %e A223956 ..0..2..2....0..1..2....0..3..3....3..3..3....2..2..3....0..2..3....0..1..1 %K A223956 nonn %O A223956 1,1 %A A223956 _R. H. Hardin_ Mar 29 2013