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 A187981 #13 Jun 15 2025 16:08:06 %S A187981 0,2,5,15,57,181,632,2199,7593,26706,93724,330555,1170088,4149361, %T A187981 14754670,52564714,187595025,670589799,2400467901,8603906865, %U A187981 30874479617,110907636467,398789645747,1435195800184,5169318396770,18633022691923,67210498566801,242590233305619,876138147816208,3166048659124955,11447024096561941,41407915745717488 %N A187981 Number of nondecreasing arrangements of n numbers x(i) in -n..n with the sum of sign(x(i))*2^|x(i)| zero. %e A187981 All solutions for n=3: %e A187981 .-1...-2...-3...-2...-1 %e A187981 ..0....1....2...-2...-1 %e A187981 ..0....1....2....3....2 %Y A187981 Column 2 of A187988. %K A187981 nonn %O A187981 1,2 %A A187981 _R. H. Hardin_, Mar 18 2011 %E A187981 More terms from _R. J. Mathar_, May 11 2023