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 A381759 #21 Mar 15 2025 04:21:36 %S A381759 1,1,3,5,11,38,182,938,4158,23384,160104,1063772,6987380,53746000, %T A381759 479965824,4182552416,35963592624,351432650816,3860219984448, %U A381759 41614300175968 %N A381759 Number of words of length 2n+1 with one 0 entry and two entries of each of 1..n so that there are exactly k numbers between two equal k's and so that the first element does not exceed the last. %H A381759 <a href="https://bbs.emath.ac.cn/thread-17154-1-1.html">Chinese BBS for the problem</a> %F A381759 a(n) = A381760(n) + A176127(n). %e A381759 a(4) = 5 since there are 5 different solutions: 131423024, 141302432, 240231413, 023421314, 041312432. %Y A381759 Cf. A014552, A176127, A381760. %K A381759 nonn,more %O A381759 1,3 %A A381759 _Zhao Hui Du_, Mar 06 2025