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 A188231 #7 Jul 22 2025 11:03:53 %S A188231 1,5,17,81,374,1818,8964,45225,231596,1202495,6313385,33473871, %T A188231 178991409,964308854,5229780968,28531772394,156491164870,862470267275, %U A188231 4774186037351,26533145487533,148001670048543,828332995017980 %N A188231 Number of nondecreasing arrangements of n numbers in -(n+2)..(n+2) with sum zero and not more than two numbers equal. %C A188231 Column 4 of A188236 %H A188231 R. H. Hardin, <a href="/A188231/b188231.txt">Table of n, a(n) for n = 1..28</a> %e A188231 Some solutions for n=5 %e A188231 .-4...-6...-3...-6...-7...-7...-4...-4...-6...-7...-5...-3...-7...-7...-7...-4 %e A188231 .-4...-5...-2...-3...-4...-2...-2...-2...-2...-1...-5...-3...-6...-3...-5...-3 %e A188231 .-1....0...-1....1....2...-1...-1...-1....0....0...-4...-1....3...-1....3...-1 %e A188231 ..4....4...-1....1....4....5....0....2....4....2....7....1....5....5....3....3 %e A188231 ..5....7....7....7....5....5....7....5....4....6....7....6....5....6....6....5 %K A188231 nonn %O A188231 1,2 %A A188231 _R. H. Hardin_ Mar 24 2011