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 A187979 #14 Sep 18 2024 08:29:01
%S A187979 0,2,7,30,144,597,2742,12148,54696,247482,1120330,5099759,23249035,
%T A187979 106285418,486878283,2234333944,10271022863,47283130811,217962771486,
%U A187979 1005958652638,4647869260260,21496269109425,99510938004788,461047642206301,2137763442289891,9919444208575431,46058149007746511,213991712768042425,994811217776431456,4627232005483362687
%N A187979 Number of nondecreasing arrangements of n numbers x(i) in -(2n-2)..(2n-2) with the sum of sign(x(i))*2^|x(i)| zero.
%e A187979 All solutions for n=3
%e A187979 .-1...-3...-4...-3...-1...-2...-2
%e A187979 .-1....2....3...-3....0....1...-2
%e A187979 ..2....2....3....4....0....1....3
%t A187979 AatE[n_, nminusfE_, E_] := AatE[n, nminusfE, E] = Module[{a, fEminus, fEplus, f0, resn}, If[E == 0, If[n == 0, 1, 0], a = 0; For[fEminus = 0, fEminus <= nminusfE, fEminus++, For[fEplus = 0, fEplus <= nminusfE - fEminus, fEplus++, f0 = nminusfE - fEminus - fEplus; resn = n - (2^E + 1)*fEminus + (2^E - 1)*fEplus; If[Abs[resn] <= (1 + 2^(E - 1))*f0, a = a + AatE[resn, f0, E - 1]]]]; a]];
%t A187979 a[n_] := a[n] = AatE[n, n, 2 n - 2];
%t A187979 Table[Print[n, " ", a[n]]; a[n], {n, 1, 30}] (* _Jean-François Alcover_, Sep 18 2024, after _R. J. Mathar_ in A187988 *)
%Y A187979 Main diagonal of A187988.
%K A187979 nonn
%O A187979 1,2
%A A187979 _R. H. Hardin_, Mar 18 2011
%E A187979 a(10)-a(30) from _Jean-François Alcover_, Sep 18 2024